In order to realize the real-time prediction of nitrogen content in the rice leaf population by using the rice leaf spectral index, the spectral reflectance of the top three fully expanded leaves (upper 1, upper 2 and upper 3 leaves were recorded as L1, L2 and L3, respectively) at the main growth stages of rice in cold region (T1 mid-spike differentiation stage, T2 jointing stage, T3 booting stage, T4 full heading stage and T5 wax ripening stage) under different nitrogen and variety differences in different years were collected. The change rule and the relationship between spectral index and leaf nitrogen content were explored. P-k, Root Mean Square Error (RMSE), Symmetric Mean Absolute Percentage Error (SMAPE), Root Mean Square Error of Calibration (RMSEC), Root Mean Square Error of Interactive Verification (RMSECV) and Residual Prediction Deviation (RPD) were used to verify the accuracy of the model. The results showed that with the increase of nitrogen fertilizer input, the leaf reflectance decreased in the visible region, while the leaf reflectance increased in the near-infrared platform. With the advance of the growth period, in the visible light region, the reflectance of L1 leaves of different varieties decreased first and then increased, and the reflectance of L2 and L3 leaves increased all the time. The sensitive bands of leaf nitrogen percentage were 500~550 and 650~700 nm. The correlation analysis of the spectral index and leaf nitrogen percentage content showed that the correlation coefficient of the spectral index of the following leaves was high in the early stage of growth, but it was the opposite in the later stage of growth. The L2 leaf index FD-NDNI in the T1 period, L2 leaf index GM2 in the T2 period, L2 leaf index Lic2 in the T3 period, L1 leaf index MRESRI in the T4 period, and L1 leaf index Ctr1 in the T5 period were selected as the best indexes to predict leaf nitrogen content in different periods. The regression equations R2 for predicting leaf nitrogen content were 0.54**, 0.60**, 0.66**, 0.62**, and 0.51**, respectively, which reached extremely significant levels. The P-k values of the validation indexes were 0.00, 0.04, 0.06, 0.01 and 0.04, respectively. RMSE were 0.39, 0.58, 0.22, 0.54, 2.56, SMAPE were 1.11, 1.41, 1.03, 1.64, 3.89, RMSEC were 0.17, 0.15, 0.13, 0.13, 0.13, RMSECV were 0.18, 0.14, 0.12, 0.12, 0.14, the RPD were 2.46, 2.19, 3.15, 1.74 and 3.01, respectively. Among them, the prediction effect of the L2 leaf index Lic2 at the T3 stage was the best. In summary, with the help of the selected spectral indicators, the nitrogen nutrition status of rice at different growth stages can be predicted quickly, non-destructively, and in real-time, and the sustainable development of high-yield and high-quality cold rice can be promoted.