The invention relates to a multi-hole polyester fiber DTY (draw textured yarn) and a preparation method thereof. According to the preparation method, modified polyester is spun to prepare the multi-hole polyester fiber DTY by the aid of a multi-hole spinneret plate; spinneret holes in the multi-hole spinneret plate are elliptically arrayed, namely, the hole centers of the spinneret holes are positioned on concentric ellipses, the concentric ellipses are series ellipses, long axes of the all ellipses are collinear, short axes of the all ellipses are collinear, the modified polyester is used for preparing a POY (polyester pre-oriented yarn) and then further processed to obtain the multi-hole polyester fiber DTY. A preparation method of the modified polyester includes the steps: performing reaction for terephthalic acid and ethylene glycol to prepare terephthalic acid ethylene glycol ester; adding the terephthalic acid and dihydric alcohol with branching chains, and performing reaction for mixture to prepare terephthalic acid dihydric alcohol ester; continuing to react to obtain the modified polyester. According to the method, prepared fibers are excellent in performance, the deviation ratio of linear density of the DTY is smaller than or equal to 2.0%, a breaking strength CV (variation coefficient) value is smaller than or equal to 4.0%, a breaking elongation CV value is smaller than or equal to 8.0%, and a CV value of crimping shrinkage rate is smaller than or equal to 8.0%.