The invention provides a lightweight reflecting mirror structure based on an additive manufacturing technology, which belongs to the technical field of optical manufacturing and comprises a mirror surface, a lightweight supporting structure for supporting the mirror surface, an outer frame for mounting and fixing the mirror surface and a back plate, the lightweight supporting structure is positioned in a space surrounded by the mirror surface, the outer frame and the back plate, and consists of a plurality of truss groups which are uniformly arranged on the back plate; the lightweight supporting structure is prepared by adopting an additive manufacturing technology. According to the light-weight reflecting mirror structure based on the additive manufacturing technology, the mirror body is designed in a back plate closed mode, internal truss design is adopted for light weight, the machining means is additive manufacturing, and truss structures commonly used in additive manufacturing and constructional engineering are introduced into the light-weight reflecting mirror, so that the strength requirement of the mirror body is met, and the service life of the light-weight reflecting mirror structure is prolonged. And the lightweight rate is further improved, and the problem that machining cannot be conducted through a traditional material reduction machining means is solved.