Abstract: Considering coexistence of the adsorbed gas and free gas in shale gas reservoir, a model for productivity calculation of shale gas reservoir by horizontal drilling in view of the desorption process of adsorbed gas was developed in this paper. The analysis of factors affecting the horizontal well productivity indicates that the productivity without the effect of natural micro?fractures is almost zero, so only those shale gas reservoirs with developed natural micro?fractures have commercial exploitation value. In the development process, the proportion of the desorption gas becomes larger and larger, the production will be higher and the stable production time of duration will be longer. So, the gas adsorption and desorption must be taken into consideration for development of shale gas reservoir. The result of orthogonal test indicates that natural fracture permeability has the most significant effect on productivity, and the occurrence of micro?fractures should be paid more attention to for it could directly determines the productivity of fractured horizontal wells