The invention discloses an oil filler cap of a car. The oil filler cap comprises an oil filler cap body and a hinge assembly. The oil filler cap body comprises a face plate and a bottom pate which are fixedly connected. The hinge assembly comprises an oil filler cap connecting plate and a car body connecting plate which are hinged through a pin shaft. The oil filler cap connecting plate is fixedly connected with the bottom plate. The oil filler cap connecting plate is provided with a first strip-shaped protrusion and at least one strip-shaped through groove. The length direction of the first strip-shaped protrusion is perpendicular to that of the strips-shaped through groove. The bottom plate is provided with a first thin and long through hole and at least one protruding point. When the oil filler cap connecting plate and the bottom plate are connected, the first strip-shaped protrusion falls into the first thin and long through hole, and the protruding point falls into the strip-shaped through groove. The oil filler cap of the car is simple in structure, convenient to machine and manufacture, capable of achieving rapid positioning of the hinge assembly and capable of achieving welding clamping, paint spraying operation and general assembly installation positioning.