Abstract: A quasi dynamical mathematical method of fault simulation and a diagnosis algorithm based on Grey Relational Analysis are given for a liquid rocket engine (LRE) system with series double turbine pump feed structure.By use of this algorithm,numerical simulations of various typical fault modes have been carried out for a certain system determined by adjustment calculation,the fault mode database for this system was obtained in advance,a group of parameters collected from the engine tests were diagnosed in real time by use of the above database and model to determine the health conditions of the engine.In consequence it is possible to take measures in good time to enhance the safety and reliability of the engine.