The heat setting of sewing thread is known to have some puckering. In this experiment, the P/C fabrec and polyester thread were heat setted at temperatures ranging from $70^{circ}C$ to $150^{circ}C$ at the interval of every $^20{circ}C$ for the period of 1, 5, 10, 20 and 40 minutes resoectivly. The results obtained are as follows: 1) In general, the pre-laundering sewing shrinkage related negatively to time but related positively to temperature. And it showed the lowest rate at $110^{circ}C$. 2) In case of slack treatment, the post-laundering sewing sewing shrinkage marked the lowest rate at $130^{circ}C$ while that of stretch treatment showed the lowest rate at $90^{circ}C$. 3) The rates of post-laundering sewing shrinkage were higher than those of pre-laundering shrinkage, the difference between them reached the bottom when applied the slack treatment at $130^{circ}C$ and the streched treatment at $110^{circ}C$.