Nowadays, Electric Vehicles (EVs) are the new technology to reduce the usage of fossil fuels and to prevent the environmental issues. But, increasing the number of EVs and mismanagement of their energy in distribution networks would cause higher operational costs and lower network security. This paper evaluates the voltage security of distribution networks in the presence of EVs. Accordingly, the maximization of voltage security margin (VSM) and the minimization of operational cost are considered as the main objective functions in the optimization problem of active and reactive power management. The constraints of the proposed optimization problem include power flow equations, system operating limits and EVs constraints. It is supposed that the EVs are equipped with bidirectional chargers to control active and reactive power, simultaneously. The proposed model is implemented on the 33-bus distribution network to evaluate the performance of the proposed optimization scheme for distribution network management in the presence of EVs.