The purpose of this study was to investigate the conversion law of dry matter and the critical period of accumulation in potato plants using the concept of convergent effective accumulated temperature, with the aim of providing theoretical support for scientific nutrient management in potatoes. In this experiment, Yanshu 4 was used as the experimental material. The whole plant was sampled continuously and dried to determine the dry matter content of each organ（leaf, stem, root and tuber）. The highest and lowest temperatures were recorded, and the average temperature was calculated. The relationship between the dry matter content, dry matter growth rate and the convergent effective accumulated temperature was analyzed. The results showed that the highest dry matter content in leaves and roots occurred at a convergent effective accumulated temperature of 883.89 ℃ ·d, while the stem and tuber reached their highest dry matter content at temperatures of 1 903 ℃·d and 1 791.15 ℃·d, respectively. The comparison of dry matter content in peak period indicated the following order: root ＞ tuber ＞ stem ＞ leaf. The R²values of the corresponding functions were 0.735 4, 0.767 5 and 0.712 1, respectively. The dry matter content of the four organs increased after the convergent effective accumulated temperature reached 1 672.42 ℃·d, and increased rapidly in leaves, stems and roots. When the convergent effective accumulated temperature reached 883.89 ℃·d, the dry matter content of leaves began to decrease and turned to tuber. During the growth process of stem, the dry matter content increased with maturity, lignification and dehydration. The dry matter content of roots stopped growing after883.89 ℃·d. The dry matter content of tuber began to increase at 1 378.9 ℃·d. In terms of the growth rate of dry matter content, the highest value of leaf appeared in convergent effective accumulated temperature of 1 000 ℃·d, stem at640-1 378 ℃·d, root and tuber at 757.31 ℃·d and 1 275.86 ℃·d respectively. Yanshu 4 entered into tuber growth stage at 883.89 ℃·d, starch accumulation at 1 378.9 ℃·d and maturity at 1 672.42 ℃·d. The best time for dry matter growth of leaf, stem and tuber was 1 029.44-1 158.07 ℃·d, 640-1 378 ℃·d and 1 275.86 ℃·d respectively.The optimal period for dry matter growth in roots was before 757.31 ℃·d.