Two-dimensional (2D) transition metal dichalcogenides (TMDCs) such as tungsten diselenide (WSe2) have spead many interesting physical properties,which may become ideal candidates to develop new generation electronic and opto-electronic devices.In order to reveal essential features of 2D TMDCs,it is necessary to fabricate high-quality devices with reliable electrical contact.We systematically analyze the effect of graphene and metal contacts on performance of multi-layered WSe2 field effect transistors (FETs).The temperature-dependent transport characteristics of both devices are tested.Only graphene-contacted WSe2 FETs are observed with the metal-insulator transition phenomenon which mainly attributes to the ultra-clean contact interface and lowered contact barrier.Further characterization on contact barrier demonstrates that graphene contact enables lower contact barrier with WSe2 than metal contact,since the Fermi level of graphene can be modulated by the gate bias to match the Fermi level of the channel material.We also analyze the carrier mobility of both devices under different temperatures,revealing that graphene contact can reduce the charge scattering of the device caused by ionized impurities and phonon vibrations in low and room temperature regions,respectively.This work is expected to provide reference for fabricating 2D material devices with decent performances.