The invention relates to a closed three-element impeller slot welding machining and robot automatic welding control method, which comprises the following steps of: turning a blank to obtain a wheel disc and a wheel cover; milling blades on the wheel disc; milling a slot body on the wheel cover; welding the wheel disc and the wheel cover into a whole through a welding robot to finish automatic slot welding of a closed three-element impeller, wherein the step of welding the wheel disc and the wheel cover into a whole comprises the following substeps of: calling a test point access subprogram and storing M test points from a welding slot in a welding robot controller; controlling a welding gun to weld corresponding blades in the impeller; calculating and correcting an angle of a rotary worktable if the count value is smaller than the preset value, and calibrating the position of the next welding slot of the impeller further; and continuously welding the next welding slot. The wheel coverand wheel disc molded lines of the three-element impeller are accurately machined, the welding slot and the blades have good centering properties, automatic welding control of the welding robot is stable and accurate, and the machining efficiency of the closed three-element impeller is improved.