A determining method for gas shield welding line energy includes the steps that the area So and datum line energy Eo of a datum weld joint are determined; the relation, namely E/Eo=S/So, of the line energy and area of the weld joint is established; when gas shield welding is carried out, a needed line energy E value is calculated; according to the calculated line energy E value, judgment is carried out. A gas shield welding test is not needed, line energy needed by gas shield welding carried out on the weld joint can be determined after calculation is carried out through a mathematical model, fitness is quite good, in this way, a lot of labor, material resources and time are saved, and welding efficiency is greatly improved.