The invention provides an automatic power control system of a grid-connected photovoltaic power station. The system comprises an intelligent power control unit and a photovoltaic power control unit, and the intelligent power control unit receives a power control instruction value, issued by a scheduling mechanism, of the grid-connected photovoltaic power station, and issues the power control instruction value of the grid-connected photovoltaic power station to the photovoltaic power control unit. The automatic power control system can track targets, set by power grid scheduling, in the whole grid, dynamically adjust the active power output of a grid-connected inverter as well as the bus voltage of grid-connected points, and effectively improves the safety and stability of the power grid; a reactive compensation control system operated in the station can be fully utilized, the reactive power of a reactive compensation device is adjusted rapidly, and the system voltage is supported; the power adjustment function of a photovoltaic inverter can be fully utilized, grid-connected requirements are satisfied, and the construction cost of the photovoltaic station is reduced; and alarm can be raised automatically to cut the feed line and further to reduce the work load of staff on duty.