As output characteristics of photovoltaic cells change with the change of environment, reasonable maximum power point tracking (MPPT) is a key in improving efficiency of a photovoltaic system. However, there is an inherent contradiction between tracking speed and steady-state accuracy in a fixed step algorithm. The traditional variable step algorithm lacks flexibility, and has a slow start speed, limiting tracking quality of MPPT. An improved variable step incremental conductance method is proposed to solve this problem. The algorithm can select a reasonable proportion coefficient for tracking according to different work locations to overcome problems in the traditional variable step size algorithm. Simulation with Matlab/Simulink shows feasibility of the algorithm under varying illumination conditions.