In the manufacturing field, the final product quality and cost are heavily determined by assembly process. As the evolution law of defect steams in assembly process has similarities with the disease propagation in SIR model, SIR model was applied to assembly process. Firstly, we give a brief introduction to the SIR model and analyze its applicability. Then the defect model of assembly process was established combined with SIR epidemic model. The extinction and persistence of defects when the basic reproduction number R ₀ ≤1 and R ₀ >1 were discussed. Next, we proofed the conclusion with theoretical derivation and simulation experiment. Finally, the disadvantages of exist model were discussed and the direction of future work was put forward.