In order to improve the efficiency of design, the parametric design of rotary locking mechanism was carried out based on the secondary development of UG. Used the function of expression to complete the establishment of parametric model of rotary locking mechanism under the UG/NX8.0 operation interface, and combined with the development tool of UG/Open MenuScript to build menu files, with UG/Open UIStyler to create a dialog box, relying on the language of Visual C# in the Microsoft Visual studio 2010 to generate a dynamic link library file (*. dll file) based on the UG dialog box. Called *. dll file through the customized menu, complete the parametric system design of rotary locking mechanism. The results show that the system can accurately, quickly and effectively complete the function of parametric modeling of rotary locking mechanism, and will provide some references to improve the rotary locking mechanism’s design, manufacturing and assembly level.