Compared with graphene (Gr) and tungsten disulfide (WS₂), the Gr/WS₂ heterojunction exhibits a greater modulation depth, owing to its strong interlayer coupling effect, and demonstrates excellent nonlinear optical properties. In this study, a Gr/WS₂ composite material nano-film is prepared via the liquid-phase exfoliation method and coated onto the surface of an etched fiber via photodeposition method, thus forming an all-fiber saturable absorber device with advantages such as a high damage threshold, large modulation region, and simple structure. The proposed device is applied to an erbium-doped fiber continuous-wave laser, and traditional soliton mode-locking with a central wavelength of 1531.34 nm is achieved. Compared with single materials, the Gr/WS₂ heterojunction under the same experimental conditions enables a narrow pulse width (5.6 ps) and higher output power (13.61 mW). These results indicate that the Gr/WS₂ heterojunction is a promising candidate for pulse laser applications and provides a solid foundation for the development of high-performance ultrafast photonic devices.