The Voltage/Var optimization power flow is calculated by the method of SQP (successive quadratic programming method), with regarding the minimum of transmission line losses as the objective functions, the reactive power flow equations as equality constrains and a set of voltage and control variables as inequality constrains. Deciding objective functions and constrains equations, the angle of voltage is not considered as constant but active power of transmission lines was considered as constant. In this paper, formulas of objective function, equality constrains and inequality constrains were deduced by constant active power. The demand on selecting initial values of iteration of this method is not strict. The results of reactive power optimization of Ward & Hale 6, IEEE 14 and IEEE30 bus systems show that this method had stable convergence.