Based on the current aviation industry standard, national standard, national military standard and international standard of resistance spot welding, the relationship between minimum nugget diameter, minimum shear strength and plate thickness in resistance spot welding of aluminum alloy,titanium alloy, steel and super alloy is summarized. The conclusion shows that for resistance spot welding of various alloys under various heat treatment conditions, there is a boundary point in the thickness range of 1.2 ～ 1.5 mm. At the left and right of the boundary point, the minimum nugget diameter and minimum shear strength are approximately linear with the plate thickness（for ultimate strength in 1 035 ～ 1 275 MPa and more than 1 275 MPa of high temperature alloy material, the thickness of 2.5 mm to the right, need to be subdivided）, at the same time, strength of materials is put forward as the principle of classification system. This conclusion can be used to predict the minimum nugget diameter and the minimum shear strength of resistance spot welding of various plate thickness of new materials and those not covered in the standard.