Aimed at disadvantages of tedious work of the Gear Transmission design, Visual Fortran is taken as the development platform, and design data are stored and managed by self-developed program and database technology. A CAD System for Gear Transmission named GTCS is researched and developed. The system integrates designing and drawing in a body, and fully uses the powerful numerical calculation function of Visual Fortran and the function of Windows interface design, as well as the secondary development function of AutoCAD and database technology, etc. The software can realize designing and calculating of involute gear transmission mechanism, automatic drawing and various kinds of results post-processing. Results show that the research results greatly improved the efficiency and quality of the design. The result documents are easily accessible by other structural analysis software (such as SolidWorks, ANSYS, ADINA, etc) and similar design software, and convenient to use for the follow-up work.