Disclosed are a porous ultra-soft superfine denier polyester fibre and a preparation method therefor. A modified polyester is spun with a multi-hole spinneret plate to prepare a porous ultra-soft superfine denier polyester fibre; the spinneret orifices in the multi-hole spinneret plate are arranged in an elliptical form, namely the orifice centres of the spinneret orifices are positioned on serial concentric ellipses,wherein the long axes of all the ellipses are collinear, and the short axes are collinear. The multi-hole ultra-soft superfine denier polyester fibre is prepared by subjecting the modified polyester chips to metering, extrusion, cooling, oiling and high-speed winding, and the preparation method for the modified polyester comprises: reacting terephthalic acid and ethylene glycol to prepare ethylene glycol terephthalate, adding a glycol terephthalate prepared by reacting terephthalic acid with branched hexanediol, and continuing to react to obtain the modified polyester. The fibre prepared by the present method has good properties, with a linear density deviation ratio of ≤0.5 percent, a breaking strength CV value of ≤ 4.0 percent, a breaking elongation CV value of ≤ 8.0 percent, and a yarn unevenness CV value of ≤ 2.0 percent.
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