The invention provides a universal subplate of a welding jig, comprising a subplate body. The four corners of the subplate body (1) are respectively provided with a hole slot (2) connected with a jig platform; the center of the subplate is provided with a big round hole (3); an inner circular plate (4) being capable of rotating in the big round hole (3) is arranged on the big round hole (3); and the inner circular plate (4) is provided with a jig fixing screw (5). The big round hole (3) at the center of the subplate is a ladder-shaped round hole with small top and big bottom; the inner circular plate (4) is a ladder-shaped circular plate matched with the big round hole, with small top and big bottom. The edge of the inner circular plate (4) has an angle graduation line. The hole slots (2)in the four corners of the subplate body (1) are in cross recess shape. When the welding jig is changed and regulated, the universal subplate is used for accurately positioning the welding jig on thejig platform; moreover, the universal subplate has good universal property, simple structure and convenient use.