The invention relates to a pulse fiber laser using a saturable absorber as an intensity modulation device, in particular to the field of lasers. In this application, the wavelength division multiplexer is optically connected to the pump source, one end of the erbium-doped optical fiber and the output coupler respectively, and the other end of the erbium-doped optical fiber, the isolator, the polarization controller and the optical modulator are optically connected in turn, and the optical modulator The other end is optically connected to the other end of the output coupler, wherein the material of the saturable absorber of the light intensity modulator is iron selenide phosphite, because iron selenide phosphite is stacked by multiple thin layers, and has Relatively high electron mobility, which makes the optical modulator made of iron selenide phosphite have excellent light intensity modulation ability, and because the iron selenide phosphite has a large modulation depth, the pulsed fiber laser The pulse time is shorter, and the light modulator made of iron selenide phosphite is lower cost.