A novel vibration isolation method using a plane grid structure is presented to meet the special demand of high-performance vibration isolation of microvibration in spacecraft. The vibration of the coupled system, which consists of the vibration source, the grid structure and the flexible support, is modeled and analyzed. The out-plane vibration equation of the grid structure in the frequency domain is obtained by using the substructure mobility synthesis principle. Based on the assumption that the coupling between the string and the beam is unidirecional, a complete description of the vibration of the beam is achieved by decomposing the dynamic tension force of the string in the vertical and horizontal directions. The vibration transmission characteristics are analyzed in terms of the synthesized model and an experimental platform is set up to verify the isolaion performance of the grid structure. The results have shown that the grid-structure is effective in vibration isolation and more than 20dB attenuation in transmission can be achieved.