Traditionally, tolerance and maintenance designs have been studied separately in manufacturing systems. An integration optimization model of tolerance and maintenance for multi-station sheet metal assembly was presented in this work. Based on the variation propagation state space model, a quality loss model of multi-station assembly processes was built. This model considered the effect of process loss. It built the function of fixture tolerance, replacement cycle and total cost. The nonlinear tolerance optimization of locating holes (slots) in multi-station sheet metal assembly was achieved. The optimization model was calculated with practical data in a vehicle body side assembly. Compared with the same type model, it’s verified correct and rational of the model in multi-station sheet metal assembly process quality control.