Abstract: Abstract: Transformer is one of the main equipment of the electricity industry. It also consume energy during the transmission of electrical energy. The transformer losses account for the largest proportion to the loss of entire power grid in our country, which are more than 60%, because of a big amount of distribution transformers in low-voltage distribution. This makes the loss of distribution transformers occupies 30% about the total loss of transformers, therefore, to develop high energy efficient distribution transformer in order to reduce the loss becomes one of the key point for power system energy saving. China's rural power grid load have characteristics such as concentrated power usage, seasonal load great changes, obvious difference between peak and valley. For the low annual average load rate, therefore it is difficult to choose the proper capacity of distribution transformers. If the capacity of distribution transformers is chosen according to the average load or minimum load, then serious overload phenomenon will happen in the peak of power consuming; If the capacity of distribution transformers is chosen according to maximum load, then it will make the transformer capacity not fully used in long time, which will cause a large unnecessary energy waste. Based on this, using adjustable capacitive transformer will not only make it running with low load under the economic state, but also make sure the transformer can supply enough power energy during the peak of consuming, which can finally realize reducing transformer overall power loss. So it is of a great practical significance to develop and design the capacitive adjustable technology of distribution transformers.According to the features of China's rural distribution network, this paper developed and designed arcless automatically adjust capacity distribution transformers with load, aimed at solving the defects and shortcomings of adjustable capacity distribution transformers without load and mechanical adjustable capacity distribution transformers with load. By analyzing the on-load capacity regulating transformer's economic operation mode, the critical economical capacity for its economic operation is elaborated; The arcless on-load capacity regulating transformer control system composed of data acquisition module, load forecasting model, switchover strategies and thyristor triggering module was designed; The switchover strategies in view of load forecasting model based on gray theory was given. The switchover strategies overcome the non-scientific and irrational of the critical economical capacity on experience and avoid the load frequently switching due to short-term fluctuations and extend the life of retulating switches. The effectiveness of the control system was verified by actual load forecast data on a single shift and the simulation analysis of switching process. Through the calculating and analyzing, the comprehensive power loss of SZ11-M-T-315(100) on-load automatic capacity regulating distribution transformer is 1821 kW·h each year, the rate of saving electricity is 15.79%.