Abstract: Focusing on the difficulty of processing the discrete variables and the small convergence region for the current deterministic methods of reactive power optimization,a new method based on complementarity constraint smooth Newton method was applied to reactive power optimization with discrete variables in this paper.In the method,the complementarity constraints sub-condtions in the Karush-Kuhn-Tucker（KKT） conditions were transformed to be a set of smooth nonlinear equations by introducing smooth relaxation function,which ensured the nonsingularity of Hessian matrix,and the nonlinear optimization problem was reconstructed as the solution of a set of smooth nonlinear equations,and solved by smooth Newton method.On this basis,the upper and lower integer bounds of the discrete variables are constructed to be complementarity constraints conditions,and embedded with smooth Newton method to approach its integer solution successively during the Newton iteration.The results of the samples demonstrate that the method proposed for reactive power optimization owns following advantages: firstly,it has large convergence region,which breakthroughs the requirement and restriction of reactive power optimization method based on the interior point algorithm that the initial point must be located in the feasible region of the system;secondly,the strategy of adopting complementarity constraints conditions to address discrete variables is simple and efficient,and can make the optimal solutions respectively for continuous variables and for discrete variables being reliably obtained at the same time.