A method for improving the quality of a polyester industrial yarn is provided. First, in the cooling process of preparing a polyester industrial yarn prepared by polyester spinning, the longitudinal height is kept unchanged, and the cross-sectional area of the slow cooling chamber is enlarged. The chamber maintains the surface temperature of the spinneret by means of heat preservation, and then uses an oil agent containing 67.30-85.58 wt % crown ether in the oiling process of polyester industrial yarn prepared by polyester spinning. Enlarging the cross-sectional area of the slow-cooling chamber refers to the cross section of the slow cooling chamber is changed from a circular shape to a rectangular shape while keeping the spinneret connected to the slow cooling chamber unchanged. The cleaning cycle of the spinneret is prolonged by 35-45%, the full package rate of polyester industrial yarn is larger than 99%.