Physiological indexes such as morphology, nutrition, growth and reproductive capacity can diagnose the nitrogen nutrition level of plants. Physiological indicators: refers to the external factors that affect the shape, nutrition, growth and reproductive capacity of plants during their development, and the indicators of their various life states: nitrogen nutrition of plants: nitrogen has great mobility in crops and high reuse rate, and it is transferred with the replacement of crop growth centers. The imbalance of nitrogen nutrition has a far-reaching impact on crop growth, yield and quality. The results showed that physiological indexes such as root depth, chlorophyll, plant hormones, enzyme activity, photosynthetic products, nitrogen rope content, plant stress index and growth days could diagnose plant nitrogen nutrition level.