The invention relates to a voltage stability constraint reactive power optimization method based on wide-area measurement information. The method comprises the first step of constructing a branch voltage stability index, the second step of improving the branch voltage stability index, the third step of determining a multi-target reactive optimization model, the fourth step of solving the multi-target reactive power optimization model, and the fifth step of conducting reactive power optimization and adjustment by means of different reactive power optimization strategies according to different operation conditions and operation requirements of a system. According to the method, the normal operation reactive power optimization strategies combining voltage stability and system operation economy and reactive power equipment adjustment strategies based on ensuring system voltage safety on the fault operation condition are put forward; because the adopted voltage stability index has high accuracy and calculation rapidity, the method can be applied to a large-scale complex electric system, and the reactive voltage control level is raised from the single-target stable-state monitoring level to the multi-target dynamic monitoring level.