A field experiment was conducted to understand the mechanism underlying the reduction in potato yield under continuous cropping. The results showed that the activity of root system, root active absorption area, and total root absorption area were reduced as the continuous cropping year inc reased. Compared with rotation cropping, the activity of root system under continuous cropping for 3, 4, and 5 years decreased by 53.71%, 66.84%, and 66.69%, respectively, and similarly the root active absorbing by 57.6%, 75.7%, and 75.6%, and the total root absorbing by 51.4%, 67.9%, and 67.6%. The total root length, root surface area, root volume, and root tip number in root diameter of 0～0.5 mm and 0.5～1.0 mm obviously increased under continuous cropping. The tuber yield was no significantly different between 1 year and 2 years of continuous cropping, while it decreased by more than 45% compared with rotation cropping for 3 years of continuous cropping. It is thus suggested that the threshold of potato continuous cropping be no more than 2 years in the target area. In addition, the reduction in nutrient absorptive capacity and the increase in root growth increase were responsible for the yield loss of potato under continuous cropping.