Abstract In this paper, the welding parameter model of resistance spot welding (RSW) of body-in-white(BIW) Al alloy plate was studied in details, and the key welding parameters that influence the RSW quality are analysed in-depth. Based on the concept of equivalent plate thickness ( S V ), simplification of nugget volume and thermodynamic theories, combined with the properties of Al alloy, the mathematical models of welding current, pressure, time were established through production data and test verification. These models reflect the relationship between key welding parameters and equivalent plate thickness. The welding current and pressure are linear with S V , and the expressions are different when S V is greater than 2. For welding pressure, there exist two critical curves according to the different yield strength of welding materials. The yield of the material lies in between and pressure can be chosen between two critical curves. The welding time is directly linear to the actual thickness of the plate. Actual welding parameters can be obtained by the models and least test, which is very important for decision of welding parameters rapidly.