Abstract: Due to advantages such as simple structure, small volume, low cost of purchasing and maintenance, Ring Main Unit（RMU）has been widely used in distribution network. However, According to the defect statistics of Guangzhou power grid, numerous cases indicate that excessive forces caused by non-standard installation transferring from T-type Cable Joint to bush can lead to fracture and seal failure, further insulation fault, which significantly reduce equipment and system reliability. In recent years, Studies on installation process’ impact on stress of RMU bushes are mainly based on maintenance experience, quantitative analysis with numerical simulation and experiment are barely performed. In this paper, three-dimensional mechanical model based on Finite Element Method（FEM）is built, and influence law of various factors on force in RMU bushes are analyzed. Meanwhile, buckling test device is set up and force in RMU bushes influenced by different factors such as overlengthen cable is measured, the experiment data shows the same trend as the simulation result. What’s more, optimal height and interphase distance of RMU bushes is obtained with calculation. Research results of this paper have important guiding significance for T-type cable joint installation process and RMU cable cabinet structure design.