Gas-liquid two-phase flow is common in hilly terrain pipelines. A combined model is proposed to model the slug initiation, capture the development of slug and calculate hydraulic parameters.Slip velocity equation and liquid mass conservation equation are the basement of the model. Build up a moving reference frame to solve the liquid mass conservation equation. Model slug initiation and development through the change of holdup. Combined with pressure drop calculation correlations and the influence of hilly terrain to calculate hydraulic parameters. Experimental date and field data(Daqing) were used to verify the model. Analysis results show that: The relative errors of most pressure drop calculated with this model were within ±17%,the relative errors of most liquid loading calculated with this model were within ±11%,the accuracy of this model is fine.