This study surveys relation between thermal shrinkage and thermal stress properties after process simulation of heat treatment with various PET filament yarns. For this purpose, 12 kinds of regular yarns and POY, 6 kinds of DTY and 5 kinds of composite yarns were experimented for investigating step thermal shrinkage, total thermal shrinkage and total thermal stress and maximum thermal stress temperature. Thermal stress and shrinkage of the various specimens treated with wet and dry heats were analysed and discussed with the conditions of heat treatment. finally, relationship between thermal stress and shrinkage of the various PET filaments such as regular yarns, POY, DTY and composite yarns were investigated with the PET filament characteristics.