Coalbed Methane (CBM) reservoir numerical simulation is an effective tool for history match and production forecast of CBM horizontal wells, while the calculation methods of numerical model are often complex and require many input parameters. In order to get a simple and accuracy of production prediction method, the steady-state analytical productivity equation combined with unsteady boundary conditions can deduce a semi-analytical model of coalbed methane horizontal wells in linear flow. According to the numerical calculation results of CBM horizontal wells and the predecessors’ research, the relationship between saturation and pressure does not vary significantly with time and space during transient flow and can be assumed to be unique for practical purposes. The corresponding approximate calculation of the water saturation can be made of formation pressure, and gas-water two phases pseudo-pressure can be obtained according to the relative permeability curve. The pressure and saturation calculation model arededuced in this paper based on the flowing control equation of CBM, and the calculation method of water saturation by formation pressure is given. It provides a calculation basis for the gas-water two phase seepage model. Compared with the results of numerical method, and the history match of two horizontal wells in Qinshui Basin, the correctness and practicability of the semi-analytical model for CBM horizontal well is verified.