In order to achieve real-time variable dressing at winter wheat jointing stage, the fertilizer quantity real-time adjustment algorithm based on fuzzy PID control was studied. To achieve the optimal control of fertilizer, the rotation speed and opening of fertilizer apparatus were real-timely adjusted online. With ITAE criterion as the fitness function, the initial values of PID controller parameters were determined based on particle swarm optimization algorithm (PSO). The algorithm combined the traditional PID control with fuzzy algorithm by acquiring the real-time parameters, such as the crop canopy real-time spectral information (Normalized differential vegetation index,NDVI), rotation speed and opening. The parameters of PID were set online and the rotation speed and opening of fertilizer apparatus were real-timely adjusted to achieve optimal control of variable dressing. Results showed that the fuzzy PID had good dynamic stability and tracking performance. A fluctuation existed on fertilizing amount during the process of fertilization. But the variation coefficient of fertilizing amount was small with the maximum value of 3.22% and average value of 2.09%, which met the requirements of field variable fertilization. In the laboratory tests, the maximum overshoot of rotation speed was about 11.96%, the maximum overshoot of opening did not exceed 14.94%, and the system precision could reach above 87%. In the field experiments, the maximum overshoot of rotation speed was about 12.80%, the maximum overshoot of opening did not exceed 14.79%, and the system precision could reach above 86%. The system had good stability, accuracy and rapidity and it was able to satisfy the agriculture technical requirements.