To meet commercialization demands, simulation replacing full-scale modal testing are used in the CZ-6C launch vehicle. High-fidelity 3D finite element model of the entire launch vehicle was obtained through direct modeling combined with model updating based on substructure-level modal test. This model, integrated with the 3D finite element model of the launcher support arms and representative models characterizing the support arm connection stiffness, was validated against upright state modal test. This approach significantly enhanced the prediction accuracy of the dynamic characteristics. Correlation analysis between simulation results and test results shows that the relative deviation of frequencies is within ±6.1%, the modal assurance criterion (MAC) values of vibration modes are at least 80.0%, and the absolute deviation of vibration mode slope is within ±0.01. This 3D model effectively reflects the rocket's dynamic characteristics, laying a foundation for design work such as flight attitude control systems, rocket loads, and mechanical environment. The technical approach taken shortens the development cycle and reduces costs.