In order to improve the conversion efficiency of photovoltaic cells and reduce the energy loss,the maximum power point tracking (MPPT) method needs to be studied. Aiming at the problem that the tracking speed and steady-state accuracy of the traditional perturbation observation method (P&O) cannot be balanced,and misjudgment occurs when the environment changes greatly,a variable-step P&O control strategy that can adapt to the environmental changes is proposed. Firstly,the short-circuit current under current illumination is obtained by using the characteristics of the photovoltaic cell similar to the constant current source when it first starts,and the reference voltage of the maximum power point (MPP) is derived by the fixed current method. Secondly,when the illuminance changes abruptly,the power correction method is proposed,and the variable step size adjustment strategy is given. Finally,a fractional order proportion integration differentiation (FOPID) controller based on linear extended state observer (LESO) is designed,which can further track and compensate the reference voltage output by the algorithm. Simulation results show that the proposed control strategy can improve the steady-state accuracy and tracking speed,and effectively improve the output power of photovoltaic cells.