The invention relates to a primary automatic-positioning accomplishment method for a connecting shaft of a hot-rolled line finishing mill group, in particular to the primary automatic-positioning accomplishment method for the connecting shaft of 2250mm hot-rolled line finishing mill group. The method comprises the following steps: when the connecting shaft rotates for a circle to detect positioning limit and the changed feedback pulse number of a main motor absolute-speed encoder during a PLC single-sweep period is less than a preset value, judging that the connecting shaft is successfully positioned, and then interrupting positioning operation of the connecting shaft; when the changed feedback pulse number of the main motor absolute value encoder during the PLC single-sweep period is less than the preset value, if a positioning limit signal is still not detected at this time, forcing a rolling mill to operate, and then searching the limit signal; if detecting that positioning limit is energized, outputting and switching a speed reference value of the rolling mill into zero immediately; and when meeting an over-constrained localization condition, ending positioning operation of the connecting shaft. The accomplishment method has the beneficial effects of avoiding insufficient localization and over-constrained localization, speeding up roller replacement, saving the time for roller replacement, and achieving normal production as soon as possible and obvious economic benefit.