The invention discloses a plate strip rolling mill scrapped supporting roll improvement method. The method comprises the following steps of (1) detecting scrapped supporting rolls and selecting the scrapped supporting roll meeting the conditions; (2) determining key technical indexes of a supporting roll ready to be improved; (3) conducting high-temperature annealing; (4) conducting semi-finish-turning; (5) conducting cooling protection on the roll neck and conducting differential temperature quenching; and (6) machining the supporting roll into a finished product according to the working procedures. The improved supporting roll obtained through the improvement method can be stably used on roughing mills and finishing mills on a production line. The millimeter rolling capacity of the improved supporting roll reaches 4-7 tons and is equivalent to the application actual performance of a new supporting roll. The improved supporting roll has no negative effects on the surface quality and dimensional precision of the product and meets the requirements for rolling of high-surface-quality plate strip products.