Abstract: A method about how to select performance parameters and monitoring parameters for fault diagnosis of turbo shaft is introduced in the paper.A means to resolve the non static fault equation is proposed.This approach is achieved due to less numbers of monitoring parameters than that of performance parameters during developing the mathematical model of fault diagnosis by introducing fault factors.The similar degree of maximum probability solutions which is the index for judging effectiveness of engine fault diagnosis after diagnosing engine health condition with given rules is given.The fault equation is separately verified either with non fault data of engine or with simulating single fault and combination of two faults.It shows that the developed fault diagnosis equation is creditable.Conclusions have been obtained that different faults can be separately diagnosed by means of selecting many adequate monitoring parameters and the effective degree of diagnosis effects can be increased by decreasing measured errors of parameters.The diagnosis system has practical value for monitoring health condition of turbo shaft on active duty and has reference usages for other engines.