This variable rate fertilizer applicator based on crop canopy real-time spectral information (normalized differential vegetation index) was designed to realize real-time variable fertilization in the field. By accessing the real-time normalized differential vegetation index via six spectrum sensors, and the speed of the tractor via velocitymeasuring system, the expert system of applicator could ascertain the rate of fertilizer based on the fertilization algorithm. The expert system of applicator adjusted fertilizing to attain precision fertilization according to the feedback fertilizer flow. The system design, working principle and experiments of the applicator were explained. The experimental results indicated that the inherent spatial variability of wheat growth within a field was considerable, and wheat canopy normalized differential vegetation index could resolve this difference. The fertilization precision could reach above 90%, and variable rate fertilizer applied more nitrogen (28kg/hm2) than quantitative fertilization. Therefore, the control system of the rate fertilizer applicator was favorable, and the applicator could achieve precise fertilization in the precision agriculture.