Through the sand culture pot experiment，using complete solution as the control, modified diagnosis and recommendation integrated system （M-DRIS） was used to diagnose the N,P,K sufficiency in different parts of N deficiency potato. The results showed that nitrogen deficiency would inhibit the growth of potato. The nutrient content of N was lower than CK(complete solution) while the nutrient content of P,K were higher. Nutrient imbalance index (NII): aerial stem＞leaf＞the petiole＞leaf blades＞tuber＞underground portion. The nutrient content of aerial stem was the most imbalanced part, while underground portion nutrient content was in a proper range. The order of nutrient requirements by potato seedlings was N＞K＞P under the condition of N deficiency.