A method of preparing a high-uniformity coloured polyester industrial yarn, wherein a modified polyester is subjected to solid phase polycondensation, metering, and adding black masterbatch; said method comprising: performing an extrusion using a porous spinneret; and after said porous spinneret extrusion, cooling, oiling, drawing, heat setting and winding, to obtain a high uniformity coloured polyester industrial yarn; wherein said spinneret comprises a plurality of orifices; wherein the arrangement of said plurality of orifices on said porous spinneret is elliptical; said elliptical arrangement being that the centre of each orifice of said plurality of orifices is located on a concentric ellipse, and the concentric ellipse is one of a series of ellipses, and the long axes of all the ellipses are arranged along a line, and the short axes are collinear; wherein the preparation process of the modified polyester includes the following steps: preparation of terephthalic acid glycol ester: mixing terephthalic acid and a branched diol to a first slurry, and carrying out a first esterification reaction under the catalytic action of concentrated sulfuric acid to obtain a terephthalic acid glycol ester; said branched diol referring to a diol having a branched chain which is a non-terminal carbon in the diols segment and a branched chain having a linear carbon chain of 5 to 10 carbon atoms; preparation of ethylene terephthalate: mixing the terephthalic acid and the ethylene glycol to a second slurry, and carrying out a second esterification reaction to obtain ethylene terephthalate; preparation of modified polyester: after the second esterification reaction in said step is completed, adding the terephthalic acid glycol ester prepared in said step, stirring and mixing, running the polycondensation reaction under the action of a catalyst and a stabilizer, and under the condition of a negative pressure; first in a low vacuum stage and then in a high vacuum stage to obtain said modified polyester. performing an extrusion using a porous spinneret; and after said porous spinneret extrusion, cooling, oiling, drawing, heat setting and winding, to obtain a high uniformity coloured polyester industrial yarn; wherein said spinneret comprises a plurality of orifices; wherein the arrangement of said plurality of orifices on said porous spinneret is elliptical; said elliptical arrangement being that the centre of each orifice of said plurality of orifices is located on a concentric ellipse, and the concentric ellipse is one of a series of ellipses, and the long axes of all the ellipses are arranged along a line, and the short axes are collinear; wherein the preparation process of the modified polyester includes the following steps: preparation of terephthalic acid glycol ester: mixing terephthalic acid and a branched diol to a first slurry, and carrying out a first esterification reaction under the catalytic action of concentrated sulfuric acid to obtain a terephthalic acid glycol ester; said branched diol referring to a diol having a branched chain which is a non-terminal carbon in the diols segment and a branched chain having a linear carbon chain of 5 to 10 carbon atoms; preparation of ethylene terephthalate: mixing the terephthalic acid and the ethylene glycol to a second slurry, and carrying out a second esterification reaction to obtain ethylene terephthalate; preparation of modified polyester: after the second esterification reaction in said step is completed, adding the terephthalic acid glycol ester prepared in said step, stirring and mixing, running the polycondensation reaction under the action of a catalyst and a stabilizer, and under the condition of a negative pressure; first in a low vacuum stage and then in a high vacuum stage to obtain said modified polyester. preparation of terephthalic acid glycol ester: mixing terephthalic acid and a branched diol to a first slurry, and carrying out a first esterification reaction under the catalytic action of concentrated sulfuric acid to obtain a terephthalic acid glycol ester; said branched diol referring to a diol having a branched chain which is a non-terminal carbon in the diols segment and a branched chain having a linear carbon chain of 5 to 10 carbon atoms; preparation of ethylene terephthalate: mixing the terephthalic acid and the ethylene glycol to a second slurry, and carrying out a second esterification reaction to obtain ethylene terephthalate; preparation of modified polyester: after the second esterification reaction in said step is completed, adding the terephthalic acid glycol ester prepared in said step, stirring and mixing, running the polycondensation reaction under the action of a catalyst and a stabilizer, and under the condition of a negative pressure; first in a low vacuum stage and then in a high vacuum stage to obtain said modified polyester.