Abstract: Low-temperature dyeing auxiliary CWL was developed in terms of compounding and synergistic technique in order to decrease the thermosol dyeing temperature of polyester fiber.The application experiments of CWL in thermosol dyeing were discribed.The colour depth of the dyed fabrics was compared between the pre-plasticizing dyeing process and one bath dyeing process with auxiliary CWL.DSC analysis was used to test the glass temperature of polyester fiber.The results show that the glass temperature of polyester fiber treated with CWL has obviously dropped,therefore the plasticization effect is confirmed.And the colour depth of the fabric dyed by one bath process with CWL at(180 ℃) is the same as that dyed by normal thermosol dyeing at(210 ℃).Moreover,the K/S value of one bath dyeing process is much higher than that of the pre-plasticization dyeing process.