Molybdenum disulfide (MoS2) holds great promise as atomically thin two-dimensional (2D) semiconductor for future electronics and opto-alectronics.In this report,we study the magnetoresistance (MR) of MoS2 field-effect transistors (FETs) with graphene insertion layer at the contact interface.Owing to the unique device structure and high-quality contact interface,a gate-tunable linear MR up to 67％ is observed at 2 K.By comparing with the MRs of graphene FETs and MoS2 FETs with conventional metal contact,it is found that this unusual MR is most likely to be originated from the contact interfaces between graphene and MoS2,and can be explained by the classical linear MR model caused by spatial fluctuation of carrier mobility.Our study demonstrates large MR responses in MoS2-based systems through heterojunction design,shedding lights for the future magneto-electronics and van der Waals heterostructures.