Experiments were carried out on the performance of the crop growth monitoring diagnostic instrument. The results showed that multi-spectral sensor had high linearity and precision, and linear correlation coefficient was over 0.95. Sensor with characteristics of good repeatability and stability, the hysteresis error of whose detection lens on 720nm was 3.35%, and on 810nm was 2.22%. And also the dynamic stability of the instrument was well. In the test environment, with the smaller measurement error caused by the solar light irradiation changes, the average error of 720nm detection lens was 1.43% and of 810nm detection lens was 1.38%. The instrument has excellent performance on monitoring leaf nitrogen content, leaf nitrogen accumulation, leaf area index and leaf dry weight , the linear regression correlation coefficient of which were 0.8795, 0. 8830, 0.8596 and 0.8393 respectively and average measurement error of which were 6.14%, 8.29%, 6.24%, 6.19% respectively.