Abstract: The spoon-chain metering device is widely used in small and medium-sized potato planter at present. Its performance is closely related with the quality as well as the efficiency in seeding operation. Because of the diced potato is used in planting in most parts of China, and their shape and size are not consistent, it is hard to take tuber in spoon and loss sowing event may occur easily. The rate of loss sowing can be reduced by optimizing the structure of metering device and the operation parameters, nevertheless, the rate of loss sowing is still around 7%. The artificial reseeding is usually adopted to guarantee the quality of planting. However, this not only increases the labor input and the operating costs, but also brings loss sowing because of the fast speed of seed metering device together with the slower reaction for a man. In order to solve the universal problem of the loss sowing in the spoon-chain potato seeding metering device, with high-performance microcontroller ATmega16 as the core, the detection system is designed, which is composed of the locating and potato monitoring module, and the automatic compensation unit consisting of the solid-state relay and the electromagnet. Locating module mainly includes small magnets and Hall sensor. When every small magnet which is fixed to the plate of the seed spoon skips over the Hall sensor, the magnetic field will be tested by Hall sensor and the information about spoon's arrival is sent to the microcontroller, and the microcontroller will launch the infrared transmitting circuit to emit infrared pulse. If there is no tuber on spoon, the infrared receiving tube will receive infrared pulse, and the electrical level of related port between detecting circuit and microcontroller will fluctuate; the microcontroller sends working instruction to the reseeding implement system according to program, and the reseeding pulse output by microcontroller is received by reseeding implement system; then, the current will flow across the electromagnet coils through the solid-state relay, and the potato seed at the entrance on the compensation way will be hit into the protecting groove under the effect of electromagnet thrust. After that, the hitting stick returns to its original position due to the function of spring restoring force. Otherwise, the reseeding implement system does not work. In order to test the performance of loss sowing detection and automatic compensation system of the chain at different working speeds, the bench test is carried out using the self-made spoon-chain test-bed for potato sowing. Spoon-chain and seed-bed belt are driven by a motor and its velocity is adjusted by inverter. The sandbox is arranged in front of the conveyor belt to simulate the movement of potato on the seed bed. The diced potato is used in the main metering system, while the micro-tuber with the diameter of 20-25 mm is adopted in reseeding system. The chain speed is set as 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8 m/s, and the number of theoretical seed metering is 1000 at different speeds. The number of total seeding, loss sowing, normal seeding, theoretical seeding and reseeding are obtained by conducting the bench test. It can be concluded that the number of theoretical seeding is the sum of total seeding and loss sowing, and the number of normal seeding is the difference of the total seeding and reseeding. The original rate of loss sowing, reseeding and final loss sowing can be calculated according to the statistical data. Among them, the original rate of loss sowing is the ratio between the number of loss sowing and the number of theoretical seeding with no automatic compensation system; the rate of reseeding is the ratio between the number of reseeding with compensation system and the number of loss sowing with no automatic compensation system; the final rate of loss sowing is the ratio between the number of loss sowing and the number of theoretical seeding. The tests show that the changes of the final rate of loss sowing and the rate of reseeding are relatively small when the linear velocity varies from 0.3 to 0.8 m/s, and the final rate of loss sowing is less than 2%, and the rate of reseeding is around 85%. The performance of the designed potato loss sowing detection system and the compensation unit is stable, and the loss sowing problem of potato spoon-chain metering device in the operation process can be solved fairly well.