Abstract: The selection of measurement parameters of engine air path fault diagnosis was researched in this paper based on the primary factor model and prediction error sum of squares(PRESS) principle.Through plenty of computing results,a method was established for fault diagnosis of one spool turbofan engine by selecting six measurement parameters,namely,corrected mass flow of fan,outlet total pressure of fan,outlet total temperature of compressor,outlet total pressure of compressor,outlet total temperature of low-pressure turbine and fuel mass low.This can also obtain satisfactory diagnosis results while the results can also be applied to other forms of aero engines.It is indicated that the reasonable type and quantity selection of measurement parameters not only guarantees the diagnosis,but also cuts down the cost.The method is of some engineering value.