Objective To introduce a computer aided navigation method of guiding intramedullary broacher in a hip joint replacement operation. The method can help surgeons to determine a proper intramedullary broacher cutting path in operations and reduce the risk of some complications, such as bone fracture. Methods First a probe was inserted into a patient’s marrow cavity and the center line of the probe was chosen as the reference path for cutting the patient’s cancellous bone. Then we placed the intramedullary broacher into the patient’s marrow cavity and took the center line of the extractor rod, which connected with the intramedullary broacher, as the current cutting path of the intramedullary broacher. At last, we adjusted the intramedullary broacher according to the reference and current cutting paths, which were shown on a computer screen. By using a prototype of this navigator, whether the difference between the reference and actual paths on a computer display consistent with the actual situation or not was verified. Results The difference between the reference and actual paths on a computer display was consistent with the actual situation. Conclusions Theoretical analysis and the experimental result show that a surgeon can determine a proper intramedullary broacher cutting path by using the method introduced in this paper. This method can make hip joint replacement operations more convenient and reliable, reduce the risk of bone fracture in operations and improve the success of implanting hip stem prostheses.