With the rising permeability of electric vehicles(EVs), EVs contain enormous schedulable potential. It will provide guidance and support for dispatchers if the schedulable potential can be accurately predicted and evaluated. Hence, this paper introduces constant current-constant voltage two-stage variable power model to describe the process of discharging and charging. Then, an evaluation method on schedulable potential considering different needs of dispatchers and users is proposed to calculate the optimal discharging and charging threshold, when the needs of dispatchers and users are both took into account. After that the evaluation model on schedulable potential of EVs in distribution network is built. According to the data of EVs operating conditions, this model is able to evaluate the schedulable potential of EVs that meet the needs of dispatchers and users. Finally, a simulation examples demonstrated the validity and correctness of the model.