The invention belongs to the technical field of power grid operation and distribution, in particular to a power grid reactive power optimization method considering a reactive power compensation cost of a distributed power supply. The power grid reactive power optimization method comprises the steps of: analyzing a reactive power service cost of the distributed power supply, collecting technical parameters of the distributed power supply, and establishing a distributed power supply reactive power service cost model; considering a node voltage constraint condition and an adjustable transformer transformation ratio constraint condition, and establishing a power grid multi-target reactive power optimization model taking minimum operation cost and minimum voltage deviation as objective functions while taking economical efficiency and safety into account; and solving the reactive power optimization model by adopting a non-dominated ranking genetic algorithm, and solving the optimal reactive power output of the distributed power supply in an optimal solution set by adopting a TOPSIS method. The power grid reactive power optimization method makes economic compensation for reactive power service of the distributed power supply, increases the income of operators while making a reactive power optimization scheduling method of the power grid more flexible, greatly reduces active grid loss and the voltage deviation of the power grid, and is conductive to increasing the economical efficiency and safety of power grid operation.