Abstract: Faba bean is one of the food legumes crops to harvest dry and fresh seeds. The manual bean harvesting has posed a great challenge on the Faba bean production with the largest planting area at present, such as high labor intensity, labor shortage, low harvesting efficiency, and lacking special machines. Current combine harvesters or grain threshers cannot fully meet the requirements for faba bean harvesting and threshing. It is very necessary to deal with the mechanized harvesting of faba bean, such as impurities, large loss, and high rate of crushing. In this study, a 4DL-5A faba bean combine harvester was designed to integrate with the cutting, conveying, threshing, cleaning, and collection. The key components of combine harvester were first analyzed to determine the working parameters of the header, threshing, and cleaning device. Then a quadratic orthogonal rotation combination test was designed to process the data by a design expert, where the impurity, loss, and crushing rate were taken as the response indexes. A field test was carried out in the Nantong test base, Jiangsu Province of China from June 13 to 15, 2020. The weather was sunny and the temperature was 32 ℃. The total area of the test base was 7 hm2. The faba bean variety was taken as “tongcanxian No.6”, where the yield per hectare was 3 000-4 500 kg, the average plant height was 852.3 mm, the average minimum pod height was 60.8 mm, and the average weight of 100 seeds was 262.8 g. An analysis was also made to explore the effects of forwarding speed, drum speed, and fan speed on the response index of the combine harvester. A regression mathematical model was established for the impurity content, loss rate, and crushing rate. The response surface method was then selected to implement the multi-objective optimization of the regression model. The results demonstrated that an optimal combination of operation parameters was achieved as follows: the forward speed 0.57 m/s, drum speed 400.45 r/min, and the fan speed 1 265.16 r/min, where the impurity rate was 3.23%, the loss rate was 3.00%, and the crushing rate was 2.72%. A field experiment then verified that the impurity rate, loss rate, and crushing rate were 3.49%, 2.87%, and 2.83%, respectively. The relative errors with the optimized values were 8.05%, 4.33%, and 4.04%, respectively. The findings can provide a strong reference for the design and optimization of structure and operation parameters in a faba bean combine harvester.