Aeroengine gas path fault diagnosis is an active process to identify the performance degradation or failure of gas path components by analyzing gas path parameters of engine system and components. It is one of the most important aspects to improve flight safety and reliability, and reduce engine maintenance cost. At present, it has become a hot topic in the field of flight propulsion technology. This paper presents the development of engine gas path fault diagnosis technology; discusses the main methodologies of engine gas path fault diagnosis, including the linear / nonlinear model based, data-driven based, information fusion based ones. The comments on the advantages and disadvantages of these methods are then followed. The key technologies and difficulties are finally pointed out, and the prospect of aeroengine gas path fault diagnosis is reached.