Provided is a preparation method of low-shrinkage polyamide 66 industrial yarn. The preparation method comprises the following steps that 1, slices enter a drying tower to be dried so as to be tackified; 2, the treated slices are subjected to humidifying treatment till the optimal moisture content and viscosity are achieved; 3, the treated slices enter a screw extruder to be heated, and melt is obtained; 4, the melt enters a spinning component, and after metering is conducted through metering pumps and filtering is conducted through filter devices, spinning is conducted through a spinneret plate under high pressure; 5, melt trickles sprayed by the spinneret plate enter a spinning channel to be cooled to form tows; 6, after cooling is conducted, the tows are oiled through an oiling roller; 7, six pairs of hot rollers conduct drafting and shaping on the tows; 8, the tows obtained after being drafted and shaped are subjected to winding on an eight-head winding device. The preparation method is high in winding efficiency and low in breakage rate, the hot-shrinkage rate of the prepared polyamide 66 industrial yarn is lower than or equal to 2%, the denier ranges from 100 D to 1,890 D, the breaking strength is higher than or equal to 9.2 g/D, and the elongation at break becomes 18%-22%.