Abstract: The thick heterogeneous gas reservoir has serious interzonal and intra - zonal interference, and the well inclination changes with the increase of reservoir depth, which is inconsistent with the assumptions of the existing productivity calculation methods. In this paper, the calculation equation of wellbore pressure loss considering the change of wellbore inclination angle and the change of wellbore flow rate is established. The calculation error of wellhead oil pressure or measuring point pressure is converted to the pressure in the middle of gas reservoir. In order to solve the problem of large difference of reservoir properties among different production layers, the production capacity of each small layer is calculated by layers, and the interlayer interference coefficient is introduced to modify the combined production equation. The calculated results are compared with the measured results, and the method has high reliability.