It has been widely accepted that the large-scale renewable energy is connected to the distribution network, but many renewable power sources and power electronic devices are liable to cause severe reactive power fluctuation, which increases the power loss and voltage fluctuation of distribution network. In this paper, a reactive power optimization method based on improved adaptive particle swarm optimization (IAPSO) for distribution network with integrated renewable energy is proposed. Firstly, the output prediction data of wind turbine and photovoltaic system are obtained by modeling. Secondly, the reactive power optimization model of distribution network with integrated renewable energy is established, which contains the penalty function of voltage exceeding limit. Then, the concept of voltage stability index is introduced to evaluate the voltage status in each period of distribution network. And the model proposed in this paper is solved by IAPSO. Finally, the improved IEEE-33 node system is used for simulation verification. The simulation results show that the proposed model can effectively reduce network loss and voltage fluctuation, and ensure the stable operation of the distribution network, which can provide reference for the subsequent reactive power optimization.