The invention discloses a low-pressure and high-power stator preformed winding welding method and relates to the manufacturing method of generator stators. The low-pressure and high-power stator preformed winding welding method solves the problems that existing junction welding is difficult, long in preparation time and large in quantity of copper used. The method comprises the steps of coiling a plurality of copper bars into single coil rings, pulling the single coiling rings to form single-turn formed coils, manufacturing a formed coil set with the single-turn formed coils, embedding the formed coil set in a stator machine base, manufacturing a cut formed coil set, manufacturing a connected formed coil set, taking the connected formed coil set out of the stator machine base for welding to form a linkage of formed coil, manufacturing single-linkage insulating formed coils, embedding an integral coil formed by the single-linkage coils in an enclosing mode in the stator machine base to form a stator winding, and splicing the single-linkage insulating formed coils to achieve stator preformed winding welding. According to the low-pressure and high-power stator preformed winding welding method, early-stage preparation work is simple, machining is convenient, labor intensity is low, copper consumption is low, splicing is firm, and the stator machine base does not need to be cleaned.