The invention provides a fixture for assembling an oil sensor sealing washer and belongs to the technical field of assembling oil sensor sealing washers. The fixture is mainly intended to solve the problems of inaccurate positioning and failure in meeting process requirements due to mounting hole sites must be visually measured when sealing washers are assembled at present. The fixture is mainly characterized by being composed of a base and two positioning pins; the base is a nylon base; two positioning holes corresponding to a sensor mounting hole in position are formed in a front portion of an upper surface of the base, while a placement groove matched with sensor oil inlet/return pipes is formed in a rear portion of the same; the two positioning pins are cylindrical copper rods with truncated cones at upper ends thereof, and lower ends of the cylinder copper rods are correspondingly fixed in the two positioning holes of the base. The fixture for assembling the oil sensor sealing washer has the characteristics that not only is the production efficiency improved, but also the sealing gasket assembling process of a product can be guaranteed, and the labor cost can also be reduced; the fixture is mainly applicable to assemble sealing washers of automobile oil sensors.