Intrinsic magnetism in two−dimensional materials requires functionalization as a means to explore their spintronic applications. In this work, first−principles prediction calculations are performed to investigate the electronic and magnetic properties of MoS2 monolayer and MoS2/Gr heterostructure by considering the concentrations of Fe−doping and S vacancy. The MoS2 monolayer is half−metallic by Fe mono−doping, while a ferromagnetic metallic state is observed by substituting two Fe dopants at the Mo−sites. Significant mechanism with total magnetic moment of 8.19 µB emerges in the MoS2/Graphene heterostructure by creating the S monovacancy and dual−Fe dopants simultaneously. The introduction of S divacancies in dual−Fe doped MoS2/Gr heterostructure results in a reduced total magnetic moment of about 6.27 µB. The further calculated spin polarizations and charge transfer give a deep understanding of the origin of ferromagnetism in MoS2/Gr heterostructure. Our results demonstrated that the enhanced magnetism can be tuned in Fe−doped MoS2/Graphene with assistant of S vacancy, providing a new pathway to extend its magnetic sensor application.