The invention relates to a low-shrinkage activated polyester industrial yarn and a preparation method thereof. The preparation method comprises: carrying out solid phase condensation polymerization tackifying on a modified polyester, melting, metering, extruding, cooling, oiling, drawing, carrying out heat setting, oiling with an activated oil agent, winding, and carrying out pre-activation treatment, wherein the oil agent for oiling contains crown ether, the content of the crown ether is 67.30-85.58 wt%, and the material of the prepared polyester industrial yarn is the modified polyester withthe molecular chain including a terephthalic acid chain segment, an ethylene glycol chain segment and a diol chain segment having the branched chain. According to the present invention, the preparation method is simple and reasonable; and the dry heat shrinkage rates of the finally obtained low-shrinkage activated polyester industrial yarn respectively are 5.5+ / -0.8% and 2.8-5.8% at the conditions comprising 177 DEG C, 10 min and 0.05 cN / dtex and the conditions comprising 190 DEG C, 15 min and 0.01 cN / dtex, and the wicking height is less than or equal to 5 mm.