With the rapid development of telecommunication, the competition of telecom market becomes more and more drastic. It is very important for telecom operator to research how to keep from the telecom churn. In the paper, a model used to simulate the behavior of customers is constructed based on system dynamics. The causal loop diagram and flow diagram of the telecom churn is proposed and some simulation results are obtained. According to these simulation results, we give some suggestions to reduce the customer churn, which are valuable for telecom operators to maintain users, formulate marketing strategies and reduce operating costs.