The invention discloses a sand box returning mechanism used for a vacuum casting line system and comprising a sand box returning line, a sand box hoisting bracket and a roller way, wherein the rear end of the sand box returning line is connected with a casting mechanism of the casting line system so that a sand box can be conveniently returned to the casting mechanism; the sand box hoisting bracket is provided with a vertically arranged guide rod and a clamping component moving upwards and downwards along the guide rod. At least one pair of clamping paws of the clamping component are respectively hinged with a clamping component body so as to facilitate the opening and closing operation. The front end of the roller way is positioned above a supporting plate returning shuttle car, and the rear end thereof is positioned above the front end of the sand box returning line. The roller way passes through the upper side of a sand dropping mechanism so as to facilitate the directional walk ofthe sand box hoisting bracket among the supporting plate returning shuttle car, the sand dropping mechanism and the sand box returning line, thereby reliably guaranteeing an operator to keep away from an area with high temperature, high silicon dust content and high danger. Based on the sand box returning mechanism, the invention also provides a returning method using the sand box returning mechanism and a vacuum casting line with the sand box returning mechanism.