PROFIBUS-DP and HART are two widely used fieldbuses, but the incompatible between them paralyzes their applications in the plants. Based on the analysis of the protocol models of the two ISO/OSI model based fieldbuses, and the study of the network structures and communication machines of the two fieldbuses. The method to resolve the incompatibility between heterogeneous fieldbuses is discussed, and an integrated approach based on gateway for the interoperation between PROFIBUS-DP and HART is proposed. The implementation, which includes hardware design and software design, is presented. The detailed SPC3 based PROFIBUS-DP interface and HT2012 based HART interface are described. And a state machine, on which the software implementation is based, is given. The test results have shown its high real-time performance and reliability.