In this paper, the effects of loading capacity and sliding speed on the tribology properties of composite films formed by a high-concentration MoS2 additive and the biopolymer hydroxypropyl methylcellulose (HPMC) are demonstrated. The main mechanisms that affect the coefficient of friction are the real contact area and the formation of the transfer layer. Reducing the real contact area will decrease the overall coefficient of friction, while the formation of the transfer layer is a dominant factor for high-load and high-sliding-speed conditions, which results in a stable coefficient of friction. The self-lubrication phenomenon occurring after the formation of the transfer layer is mostly responsible for the excellent tribology properties of the MoS2/HPMC composite material.