The invention discloses a reactive power optimization method of a distribution network including distributed power supplies. The method comprises: conventional technical parameters of a distribution network are collected and thus historical distributed power output data are obtained; with consideration of two-stage adjustment modes of a slow adjustment variable and the flexibility adjustment variable in the distribution network, a slow adjustment variable decision-making plan that can meet the operation security requirement of the distribution network and ensure the economical efficiency in all extreme scenes of the distributed power output is found out. According to the invention, the extreme scenes of the distributed power output are obtained based on historical power output prediction values and prediction relative errors and then the slow adjustment variable decision-making plan is provided, so that the randomness of the distributed power output is dealt with by the flexibility adjustment variable on the premise that the safe and reliable operation of the system is guaranteed. Therefore, the potential safety hazard of the operation of the distributed network due to the randomness of the distributed power output is eliminated; the operation network losses of the system are reduced and the clean energy consumption is increased; and the safety and economy of the power system operation are improved.