The invention provides a method of guaranteeing the product percent of pass of a low voltage surge arrester with a built-in hot melting isolating assembly and belongs to the field of arresters. By adopting a threaded connection structure, the built-in hot melting isolating assembly and a ground lead are fixed to the lower end surface of a lower pole plate, so that a reliable mechanical fastening effect and a circuit connection function between a metal core wire and a metal sleeve base of the ground lead with the built-in hot melting isolating assembly are achieved, and an automatic hot meltingdisconnection function and a quick fall-off function of the ground lead are achieved when the low voltage surge arrester fails inside, so that the arrester can quit operation automatically. The assembling quality is stable, so that the production efficiency of the low voltage surge arrester with the built-in hot melting isolating assembly is improved, and the product percent of pass of the low voltage surge arrester with the built-in hot melting isolating assembly is ensured. The method can be widely applied to the fields of design, manufacture or operation and maintenance of low voltage surge arresters, the working voltages of which are below 1 to 0.5 kV.