Abstract: Thermal power units play a critical role as primary frequency regulation(PFR) resources in new power system, with their PFR performance heavily influenced by the dynamics of steam turbines. However, existing dynamic mathematical models of steam turbines fail to accurately assess the PFR capability of thermal power units under various PFR technologies and operating conditions. To precisely assess the PFR dynamics of thermal power units, a steam turbine model is established in this paper by analyzing the dynamic coupling characteristics of the turbine body, regenerative extraction pipes, and regenerative heaters. This model is well-suited for analyzing PFR technologies such as main steam valve adjustment, condensate throttling, and feedwater bypass. Additionally, an online parameter identification method based on structural data and measured data from the distributed control system is proposed. Finally, the actual 600 MW units are taken as examples for model verification and simulation analysis. The results indicate that the output power is greatly affected by the dynamic coupling characteristics of the turbine body and regenerative system, and the PFR capability of the unit varies significantly under different operating conditions. The proposed model can describe the dynamic response characteristics of steam turbines under various PFR technologies and operating conditions more accurately.