Take example for the fault diagnostic system for shipboard chemical defense equipment, it is developed, applied virtual instrument technology, grey system theory, and database, in order to update entirely the means of the equipment testing. The modularization and universalization are proposed in its database-based design concept, realizing the design of software and hardware. The ODBC technique is applied for the interconnection of databases to ensure the generality and flexibility of the system. The system mode the best of virtual instrument platform and grey diagnosis method, broke through conventional check diagnosis patterns for warships chemical defense equipment, solved the problems of state prediction and trouble-mode recognition of warships chemical defense equipment. It has been proved by experiments that the system has merits both high accuracy and economical practicability. Also it can reduce the application development cycle and cost.