Abstract: A new ground system EMD (Engine Monitoring and Diagnosis System) has been developed which has the capability of fault isolation with only the measurements of limited monitoring due to new developed diagnosis algorithms.The output information of a limited monitoring system,as ECMII or ADEPT is transferred into the EMD system as input data.Main functions of the EMD are engine health monitoring and sensor fault identification,engine gas path module and subsystem fault isolation,engine condition comprehensive evaluation,engine parameter prediction and take off exhaust gas temperature margin monitoring.For engine health monitoring,a series of threshold values are used to judge the engine condition for each flight.A quick looking algorithm and the judgement criteria are used to identify the sensor fault.An advanced diagnosis algorithm main factor model has been developed to solve a set of linear equations for engine gas path and to obtain the estimations △x of 28 component characteristic parameters and false diagnosis risk α on the condition of 4 known measuring parameter deviations.