A typical gantry system comes with heavy components and a large size. The weight and size bring difficulties in manufacturing, transport and installation, which limit the broader application of heavy ion gantries. Moreover, a lightweight gantry design could reduce the construction costs, as well as the maintenance expenditures. To address the weight associated challenges, this paper presents a light-weight design and test scheme of a heavy ion gantry, including a lightweight beam transport line based on the combined-function superconducting magnet and the dual-direction hybrid scanning magnet, resulting in a significant weight reduction compared to the beam transport line with room-temperature magnets and normal scanning magnets. As well as an optimized main structure of the gantry through the zero-order method, with a lightweight design of ancillary equipment, resulting in 165 tons of total weight. Following the improved design, an engineering prototype was manufactured and tested to validate the lightweight design strategy. Experiments of the prototype demonstrated that the gantry met the accuracy requirements, thereby confirming the feasibility of the systemic lightweight design.