To get a general mapping algorithm for any BPD(Business Process Diagram),depth-first traversal algorithm based component is designed to deal with any BPMN(Business Process Modelling Notation) model which is composed of the tasks, events, parallel join gateway, parallel fork gateway, databased XOR decision gateway and XOR merge gateway mapping BPEL. The generated BPEL code has good maintainability and extensibility. The algorithm is implemented in the SWF system developed by Python and its validity and usability has also been proved in practical application.