The invention discloses an automation grouting tool based on a prefabricated building and a construction method thereof, and belongs to the technical field of prefabricated concrete building construction. The automation grouting tool includes two transverse bracings, a shaper and a material receiver, wherein the transverse bracings are arranged in parallel, sliding wheels arranged at the bottoms of the transverse bracings, and propulsion mechanisms arranged at the rear ends of the transverse bracings; the shaper is connected between the two transverse bracings, the whole shaper is in a cube shape, the bottom of the shaper concaves to the top direction to form a groove with a trapezoidal section, two steel channels are reserved on the shaper in the vertical direction, and the steel channelsare arranged in the length direction of the shaper in an overall length mode; and the material receiver is arranged between the transverse bracings and connected with the front end of the shaper. Theautomation grouting tool is not be affected by a reserved steel bar in the process of grouting construction, the construction efficiency is greatly improved, bottom concave of the shaper forms the trapezoidal groove, the grouting construction quality is improved, operation is simple, control of the dosage of grouting materials is convenient, grouting construction of a prefabricated wall body of the prefabricated building is optimal in one time, and material waste is reduced.