Abstract: In response to the problem of poor adaptability of welding carts to workpieces with variable curvature radii, theoretical research was conducted to improve the driving system of welding carts. A mechanical model of welding carts under sloping conditions was established, and the variation law of traction force during the movement of welding carts was analyzed, providing theoretical support for the design of welding carts. On this basis, the passability of the welding car under external and internal curved surface conditions was studied, and the minimum curvature radius that the welding car with specific structure and size can pass through under two special working conditions was calculated. Based on the above analysis results, a welding car based on friction transmission was designed and verified through simulation. The results showed that the welding car has good passability on the variable curvature radius track, which can provide technical support for the design of the welding car.