In order to improve the automation level of potato harvesting machinery, improve the potato obvious rate and reduce the injury rate and undug rate, with the traction-type potato harvester as the carrier, an automatic depth control system designed. Sensor and microprocessor control technology was used. The system included the front profiling device, the digging mechanism, the hydraulic device and the control system. Using the excavation depth real-time adjustment algorithm, the excavation depth adjustment model was established, and the precise control of the harvester excavation depth was effectively realized, and the harvest performance index of potato crops was improved. Finally, test was carried out to verify the effectiveness of the automatic depth control system. According to the growth depth of sweet potato, the initial excavation depth was 260 mm. The machine harvested six ridges with automatic depth control device and six ridges without the device. Harvest trials were performed interlaced and a total of 12 ridges were harvested for comparative test, and the harvest speed was 1.4~1.6m/s. The test results showed that with manual depth control the average potato obvious rate was 95.17%, the average injury rate was 2.90% and the average undug rate was 3.59%. With the automatic depth control the average potato obvious rate was 97.37%, the average injury rate was 1.49%, and the average undug rate was 1.59%. Through comparison, it can be seen that after the use of automatic depth control device in the harvest process, the average potato obvious rate was increased by 2.20 percentage points, the average injury rate was decreased by 1.41 percentage points, and the average undug rate was decreased by 2.00 percentage points. Harvest performance indicators exceeded the qualified value requirements. It can be seen that after the 4UGS2 double row potato harvester was installed with the automatic deep control device, it can change the excavation depth according to the change of the bottom of the ridge. The harvester can improve its operation performance index, reduce the loss in the harvest process, and thus increase the economic benefits.