During the dynamic voltage and reactive power control in substation, if not controlled, the switching action of each regulation device is too frequent, which may not only increase the failure rate of the system, but also reduce the service life of each device. Therefore, according to the requirements of actual substation voltage and reactive power dispatch, this paper proposes a control method for the dynamic substation voltage/var optimization. Firstly, considering the voltage constraints at the low voltage side, power factor constraints at the high voltage side, reactive power compensation capacity constraints and switching operation constraints, the optimization model is established with the allowable deviation of secondary bus voltage and power factor of the main transformer as control objectives. Secondly, the discrete monkey algorithm is used to solve the model. In order to improve the computational efficiency, the dynamic step size is introduced to improve the algorithm. The simulations show that the proposed method can meet the operation requirements of substation.