A method for measuring temperature of an object using the longitudinal mode output by a short cavity fiber laser, includes steps of: a) arranging the short cavity fiber laser, which laser comprises sequentially coupled laser diode pumping source, a wavelength division multiplexer, a fiber bragg grating, an active optical fiber and a loop mirror which are; b) contacting the short cavity fiber laser with the object whose temperature will be measured; c) measuring the drift amount of longitudinal mode output by the short cavity fiber laser; and d) calculating the temperature of the object to be measured. According to the present invention, the temperature can be measured accurately utilizing the features of the short cavity fiber laser. The arranged fiber laser has a small and simple structure, high measuring accuracy, good portability, and can be used in a variety of occasions.