The utility model relates to a plastic fuel tank cover of an engineering van. The plastic fuel tank cover comprises a fuel tank oil-filling port, a pressure-bearing disk, a pressure spring, an air inlet valve assembly, a plastic locking rod, a plastic housing cover and a handle pull rod. Interference fit sealing is achieved between the plastic locking rod and the plastic housing cover via an O-shaped rubber ring. The air inlet valve assembly comprises an air inlet valve, a cover-shaped gasket, a negative-pressure spring and a rubber sealing pad. A valve rod of the air inlet valve penetrates through an installing hole of the air inlet valve of the pressure-bearing disk. The cover-shaped gasket is mounted on the valve rod of the air inlet valve. The negative-pressure spring is arranged between the cover-shaped gasket and the pressure-bearing disk. The rubber sealing pad is fixed at the circular shape of a bottom surface of the air inlet valve. When a balance is stricken between internal air pressure in a fuel tank and external air pressure, the rubber sealing pas is adhered to the pressure-bearing disk for sealing and the fuel tank oil-filling port is adhered to the pressure-bearing disk for sealing. The plastic fuel tank cover of the engineering van has following beneficial effects: key problems occur when rainwater enters a fuel tank of a conventional engineering van in operation including rusting, corrosion of the fuel tank and easily-blocked air vents of the air inlet valve, clamping stagnation, automatic flameout or incapability of starting an engine are solved.