The invention discloses a MPPT strategy of a partial overshadowing photovoltaic system based on ant colony optimization and variable step size disturbance observation algorithms. According to a MPPT method, the problem of searching a global maximum power point when multiple peak values occur in the photovoltaic system under a partial overshadowing condition is solved. When a proper situation appears, the early stage of photovoltaic output is tracked by virtue of an ant colony algorithm, so that the phenomenon that the trapping of a system in a partial maximum power point by a disturbance observation algorithm is avoided, and meanwhile, the convergence speed is increased. After the secondary iteration of the ant colony algorithm ends, the algorithm is stopped, the later stage of the photovoltaic output is tracked by virtue of the variable step size disturbance observation algorithm, and the steady-state oscillation of the system caused by the ant colony algorithm is avoided by virtue of the robustness of the variable step size disturbance observation algorithm. Finally, the global maximum power point of the partial overshadowing photovoltaic system can be rapidly, accurately and stably tracked.