Abstract: Near the wellbore of a Horizontal well, there also exist damage zones, besides, it is in heterogeneous distribution and affected by the anisotropy of strata. Therefore, it may impact the productivity of the horizontal wells. This paper proposes a flowing physical model for the acidizing zone near the wellbore, based on the heterogeneous distribution of skin factor along the wellbore, by which a formula for the skin factor after acid treatment is given through considering the fact that the acidizing radius is greater or less than the radius of damage zone. According to the formula, the Joshi’s productivity formula is modified, meanwhile, the influences of horizontal section length, strata anisotropy coefficient, damage zone permeability and the maximum distance of mud immersion zone on the acidification effect are studied. It is concluded that horizontal section length, gas layer thickness, strata anisotropy coefficient, damage zone permeability and the maximumdistance of mud immersion zone are the main factors that affect increase productivity after the acid treatment of horizontal gas wells