The invention relates to a reactive power optimization method based on a complementary constraint decoupling Newton method for a high-voltage transmission network. The method comprises the following steps of S1, constructing a target function and a constraint condition; S2, constructing a decoupling mathematical model of reactive power optimization according to the target function and the constraint condition in the step S1; S3, processing the decoupling mathematical model in the step S2 by using a decoupling Newton method; and S4, solving the decoupling mathematical model in the step S3 by using a smooth Newton decoupling algorithm. In the method, PQ decoupling processing is introduced according to an active-reactive (PQ) weak coupling characteristic of a high-voltage power system so thatdimensionality of an equation set which needs to be solved can be greatly reduced, and a calculation speed is increased.