Abstract: In injection molding, the residual stress and shrinkage of the product are affected by processing conditions directly.A detailed linear thermoviscoelastic model was developed to calculate thermally and pressure induced residual stress and shrinkage in amorphous plastic parts.A systematic study on the effect of processing conditions on shrinkage and residual stress was made for PS and ABS.The results showed that the shrinkage for amorphous polymers was constant along the flow path, and the residual stress distribution through the thickness was almost the same in the flowpath, with a little higher stresses near the end.It indicated that the holding pressure was the key parameter, an increase in holding pressure and melt temperature caused a decrease in shrinkage and the effect of mold temperature on the shrinkage was much smaller.