The recognition of unusual customers is one of the most important applications in data mining. Taking an example from telecom trade, this paper presents a kind of classification and regression tree algorithm to recognizing unusual customers in telecommunication trade databases (TCART for short). The TCART includes the following process: maximal classification tree construction, regression pruning and optimal classification tree selection. During the procedure of classification tree growing, we propose a kind of improved classification approaches. Finally, TCART algorithm is validated by large numbers of customer data in Zhejiang telecom database. The experiment results indicate that TCART algorithm has the virtues of robustness and effectiveness.