Abstract: Spherical radius is a very important factor which can affect the quality of spot welding.After solving the contact problem, an axial symmetry model to simulate the welding process was established.Effects of spherical radius of electrode on low-carbon steel resistance spot welding nugget size were investigated quantitatively through ANSYS software.Nugget sizes were simulated by adopting different eletrode radius, and accuracy of simulation was verified by welding experiment. Results indicate that electrode spherical radius has great effects on the nugget diameter and penatration rate, while has few effects on the size of heat-affersted zone.Results also show the error is less than 10% between simulated value and test value.