The Inertial Navigation System (INS) is an important part of the navigation and pilot System of certain type of airplane. Developed with LabWindows/CVI and its device-oriented, interactive C language, a testing instrument based on the Compact PCI bus technology for the INS is developed. It realizes independent guarantee, quick testing and rapid maintenance. This paper introduces the overall design, emphasizing on the development of software that adopts the multithread application technology, especially the realization of the critical technology.