For the study of maximum power point tracking (MPPT) control, many existing research methods can exhibit effective output which depend on uniform solar irradiance. However, multiple peaks can be exhibited on the characteristic curve of the PV array under partial shading conditions (PSC) due to the effect of the bypass diode. In this case, the efficiency of the conventional MPPT methods are limited and the others are difficult to apply in engineering due to cost issues. In this paper, an improved hysteresis comparison method that combines with a constraint function is proposed. The performance of the proposed method is validated through MATLAB/Simulink simulations.