Abstract: Real time thread library is very important for building real time middleware. It is helpful for the portability of distributed application which possess time critical aspects. Mutex and synchronization mechanism to protect priority inversion is the key for real time thread library. Based on priority inheritance protocol, a muti thread mutex algorithm is presented, which can prevent deadlock and priority inversion. All the properties of the algorithm are proved correct including mutex, deadlock and priority inversion. In Windows and Solaris, the performance is analyzed. At the same time, this algorithm has been adapted in real time CORBA application successfully.