The invention discloses a method for predicting a transistor fault. The method belongs to the technical field of transistor damage prediction methods, and solves the technical problem of failure of apredicted transistor due to thermal fatigue. The method comprises the steps of: acquiring conduction voltage drop data and junction temperature data of a transistor, and determining a first corresponding relationship between the junction temperature data and the conduction voltage drop data; determining remaining service life of the transistor according to the first corresponding relation; acquiring servicing time data of the transistor and a second corresponding relation between the working time data and the remaining service life data; and determining economic life data of the transistor according to the second corresponding relationship, judging whether the economic life data is greater than economic life data corresponding to the transistor in a critical saturation state or not, and ifso, judging the junction temperature corresponding to the economic life data as a temperature point of thermal fatigue failure of the transistor. The method is used for completing the use function ofthe transistor, and meets the requirements of people for estimating the thermal damage of the transistor.