Abstract: Multithread technology has been adopted in recently developed mainstream operating systems. Firstly the basic concepts of multithread are described. Secondly, three implementation methods of multithread mechanism that is user\|level threads, kernel\|level threads and combined approaches are discussed. Thirdly, application of multithread programming is introduced. Through the object\|oriented database management system NODBMS, how to use multithreads to realize multiple transaction processing is also introduced, and is proposed an effective query optimization algorithm of object\|oriented database system based on multithread technology.