Spoonchain metering is the most widely used metering device in small and mediumsized potato planter at present because of its high reliability, low cost and adjustable plant spacing. Its performance is closely related with the planting quality. However, spoonchain metering still encounters loss sowing problem, which can be reduced by optimizing structure and parameters of metering device. Nevertheless, the rate of loss sowing is still around 7%. Artificial assistance metering can resolve these problems effectively but with increased labor intensity and hidden danger. In order to solve this problem, a loss sowing detection method based on capacitance value precision measurement technology was proposed in this paper, and an automatic reseeding system was designed which was mainly composed of control system, capacitance sensor and reseedmetering device. In order to test performance of the automatic compensation system, a performance test was carried out using selfmade device. Spoonchain was driven by a servo motor and its speed was adjusted by servo driver. Reseedingchain was driven by a servo motor and its speed was controlled by PLC controller. Micro potatoes, with diameter of 25~30mm, were used in main metering system and reseeding system. The metering speed was set as 0.3, 0.4, 0.5, 0.6, 0.7m/s, and the number of theoretical seed metering was 600 at different speeds. By mounting a laser sensor on seed discharge hole, the number of normal seeding and reseeding were recorded by PLC automatically. Total seeding, loss sowing, normal seeding, theoretical seeding, reseeding rate, original rate and final rate of loss sowing can be calculated. The tests showed that, with the metering speed increasing from 0.3m/s to 0.7m/s, the original rate of loss sowing, the final rate of loss sowing, the metering row spacing error and the reseeding row spacing error were increased from 7% to 11.3%, 1.1% to 1.75%, 3.3% to 9.1% and 7.6% to 16.9%; with the increasing of chain speed, changes of reseeding rate were relatively small, and the final rate of loss sowing was less than 1.75%, and rate of reseeding was around 84.6%. The performance of the designed compensation system is stable, and the loss sowing problem of potato spoon-chain metering device can be solved well.