The increase of system loss and voltage out-off-limit caused by the massive access of distributed power sources such as photovoltaic and wind turbine bring new challenges to the secure and economical operation of distri-bution networks． This study put forward a decentralized reactive power control strategy for distribution systems to address this problem．According to the strategy，each distributed generator only regulate the reactive power accord-ing to the local synchronous phasor measurement data and the low-voltage alarm broadcasted by the surrounding load buses to minimize the total active power loss and maintain nodal voltages in the system． The proposed strategy estimates the sensitivity of the system loss with aspect to local reactive injection according to the linearized distribu-tion network model using the local voltage phasor measurement． Then it minimizes the total active loss with local re-active power control． The optimal voltage support strategy for load buses by distributed generators is presented to re-pair the low-voltage of load buses with the minimum power loss cost． As compared with the existing distributed re-active power regulation strategy based on feedback control，the proposed strategy can minimize the system loss with local reactive power control，so there is no communication requirement between distributed generators． After receiv-ing the low-voltage alarm of the load buses，the low-voltage can be maintained by only one regulation，so there is no need to monitor the load node's voltage for a long time．