In the traditional primary frequency regulation model power network and main pressure of boiler constraints are ignored, and power output-frequency response is taken as linear because it overlooks the influence of main pressure on power output. In this paper, primary frequency regulation (PFR) dynamic model based on power network is established by fully considering relationship and restriction among boiler, steam turbine, load and power network and nonlinear relation between power output and frequency deviation. This model can be used to analyze the contribution of each part of network to frequency stability and embody PFR ability of generator, load and power network. The results of an IEEE 30-bus test system are studied to illustrate the proposed framework. By comparing with the PFR stable calculate results, the characteristics of proposed model is indicated, and differences among mid-term and long-term stability model, conventional transient stability model and the proposed model are investigated.