Electro-mechanical coupling facts about transmission system influence dynamic characteristic and response characteristic of servo system. The coupling factors of precision transmission system are put forward, and the modelling methods of electro-mechanical system are analyzed. Based on the large-scale precise horizontal machining center, the dynamic chart of servo feed system is gained through analyzing mathematical model of the taehes, and the influence on transmission stiffness and transmission error is simulated in precision transmission system. Through changing parameters in servo feed system, the influence on dynamic characteristic and response characteristic is analyzed, so it provides a mathematical model for parameter optimization.