|Under partially shaded conditions, the P-U curve of PV array contains multiple extreme points. General MPPT methods may misjudge the MPP and trap in the local extreme point, which will cause low working efficiency. Although the traditional PSO algorithm can accurately track the maximum power point under this condition, the optimizing process fluctuates obviously and the tracking speed can be improved. In order to solve these problems, an improved PSO algorithm is proposed. The initial positions of the particles are located by analysing the relationship of the I-U and P-U characteristic curves. It is more closed to the maximum power point. So the efficiency of PSO algorithm is improved. To evaluate the effectiveness of this method, the simulation model is established in MATLAB/Simulink. Under partially shaded conditions the algorithm can track the maximum power point quickly and accurately.