The present invention relates to a thermal-wet comfortable polyester fiber FDY yarn for summer use and a preparation method therefor, wherein the preparation method comprises: subjecting a spinning melt to metering, composite spinneret plate extrusion, cooling, finishing, stretching, thermoforming and winding to prepare the thermal-wet comfortable polyester fiber FDY yarn for summer use. The material thereof is a polyester with a dispersed matting agent, and a woven fabric made therefrom has a wicking height of ≥135 millimeters, and has an evaporation rate of ≥0.22 grams/hour. The composite spinneret plate is provided with both cross-shaped spinneret holes and circular spinneret holes, the ratio of the length of the micropores of the cross-shaped spinneret holes to the length of the micropores of the circular spinneret holes is equal to the product of the equivalent diameter ratio and a coefficient K, the range of the value of the coefficient K being 0.97-1.03. A finishing agent for finishing contains a crown ether, with the content of the crown ether being 67.30 wt% - 85.58 wt%. The preparation method of the present invention is simple, and the fibers obtained thereby have an excellent thermal-wet comfort performance and a good application prospect.