The invention provides a detection device and method for sensing arm optical fibers of an interference type optical fiber hydrophone and belongs to the technical field of optics, aiming at solving theproblems that temperature strain distribution of sensing arm optical fibers of an optical fiber hydrophone with a Michelson interference structure cannot be measured at present. An optical fiber coupler receives laser output by a laser device and laser is divided into upper and lower paths through the optical fiber coupler; the upper path is pump light and the lower path is detection light; an output end of the upper path of the optical fiber coupler is connected with an input end of a first electro-optic modulator; meanwhile, the first electro-optic modulator is used for receiving electric pulse output by a signal source; the laser is modulated through the first electro-optic modulator and is changed into pulse light and then the pulse light is input into a polarization scrambler; then the pulse light is amplified through an erbium-doped optical fiber amplifier and is input into an optical fiber circulator; finally, the pulse light is input into an interference type optical fiber hydrophone to be detected through a first port of the optical fiber circulator. According to the detection device and method for the sensing arm optical fibers of the interference type optical fiber hydrophone, provided by the invention, the temperature strain distribution of the sensing arm optical fibers of the optical fiber hydrophone with the Michelson interference structure can be detected.