As efficient and low-pollution alternative fuel, dimethyl ether (DME) has shown its excellent performance of combustion and emissions. There is a phenomenon of DME gasification in the in-line fuel pump of DME-diesel engine. DME gasification can result in “vapor lock” and serious inequality of the fuel supply in DME-diesel fuel system.This paper presents a simple solution to improve DME gasification in DME-diesel fuel system. The key feature of the solution is just a bypass check valve, which is assembled between the intake fuel supply and the plunger chamber of the in-line pump. DME gasification in the in-line pump can be effectively eliminated by means of the bypass valve design.The feasibility of the solution design is validated against AVL-HYDSIM simulations of both fuel systems, including the baseline of DME-diesel duel fuel system and the fuel system with the bypass check valve, on factors such as intake fuel pressure, DME content ratio, engine speed, DME vapor pressure and so on.The research shows that (1) the design of the bypass check valve is one solution to eliminate DME gasification in the in-line pump fuel-injection system, and (2) DME gasification is inevitable in the plunger chamber of the in-line pump due to the powerful vacuum suction of the plunger, and (3) there is less effect of intake fuel pressure and DME fuel content ratio on the elimination of the gasification in the in-line pump, because the cause of DME gasification is the structure of the plunger and barrel assembly in the in-line pump fuel-injection system.