Abstract: Based on non-back trace backward chaining Web Services dynamic composition framework, this paper proposes a backward chaining dynamic composition method to lower the execution price. In order to generate this synthes is program dynamically, the Web Service with minimal execution price is found in each step of the composition course of the algorithm based on user input/output and the execution price of Web Service. The composition approach takes into account the efficiency and execution price, so it is especially suitable for users who have requirements on the both.