The maximum power point tracking（MPPT in short）algorithm shall be added into photovol-taic power generation system because of influence of such external factor as solar radiation and tem-perature. For easing the contradiction of its tracking speed and accuracy

improving power transfer capability of system

a kind of improved type perturbation observation MPPT algorithm is proposed on the basis of analyzing photovoltaic array mathematical model and output characteristics. The voltage perturbation step is determined in accordance with the variation direction of PV array output power. The bigger fixed step in case of far away from the maximum power point is adopted and the gradually reduced step is adopted near the maximum power point. It is shown by the result that the improved algorithm can track accurately PV array maximum power point and solve effectively the contradiction between maximum power tracking speed and accuracy.