The invention discloses a prefabricated assembled building casting net and a mounting method, relates to the technical field of building construction, and aims to solve the problems that a conventional protecting casting net is complex in mounting, high in material consumption and high in cost. The prefabricated assembled building casting net is arranged around an outer prefabricated assembled building wall in an adhesion manner at a certain interval from bottom to top and comprises a horizontal rack body and a net body, wherein the horizontal rack body consists of a plurality of cantilever rod parts which are assembled in parallel at intervals; the cantilever rod parts are formed by two sections of standard knots which are moveably connected; the net body is laid on the upper surface of the horizontal rack body and is fixedly connected with a horizontal rack body frame; an included angle alpha is formed between the horizontal rack body and the outer prefabricated assembled building wall; alpha is greater than or equal to 70 degrees and less than or equal to 80 degrees. According to the mounting method, a prefabricated assembled building is assembled layer by layer from bottom to top at certain intervals according to the progress of assembling the prefabricated assembled building wall, the folded casting net can be mounted after the prefabricated assembled building wall at a preset height is assembled and is clung to the outer surface of the outer wall.