Some variables in a constraint-based configuration model may not have any immediate or indirect relationship between them; therefore, these variables will never intervene with each other in a constraint propagation. According to this characteristic of configuration, this paper proposes a preprocessing approach based on equivalent class partition, which can be used in the process of building the product model, so that the original configuration problem can be effectively divided into several sub-problems, and these sub-problems can be solved independently. The two backtracking-strategies are used in testing this method. The experimental results show that this method can effectively improve searching efficiency. Moreover, the method is integrated with the QUICKXPLAIN algorithm to compute conflict explanations, and the result show that it can also improve the efficiency of the algorithm.