Abstract: The cooling and shrinkage induced self tightening contact characteristics of polymer micro-mechanical rotating motion pairs made by in-micro mold assembly plays a key role in controlling the factor of their movable performance. The prediction and accurate control of self-tightening contact characteristics is a technical key for in-micro mold assembly.Based on the thermo-viscoelastic-plastic constitutive relation obtained from experiments,a simulation method was established for the micro assembly interfacial self-tightening thermal viscoelastic-plastic contact characteristics of the motion pairs during the molding process.The simulation results indicated that the maximum magnitude of interference, the clearance magnitude and the driving friction resistance torque of the micro assembly interface had a linear positive correlation with the secondary molding injection temperature. The reduction of the secondary molding injection temperature effectively improved the micro assembly interfacial fitting precision of micro mechanical motion pairs and also greatly reduced the minimum driving friction resistance torque to make the micro mechanical rotating pairs achieve the movable performance. When the secondary molding injection temperature decreased from 503 K to 463 K, the driving friction resistance torque of motion pairs decreased by 34.9 % from 3.61 N·mm to 2.35 N·mm.