Qi Chengwei's formulae consists of the two formulae for predicting horizontal well productivity, proposing at first time in the world; the formulae is only for the prediction of ribbon-shaped petroleum reservoir, but not for the prediction of natural gas reservoir. In order to predict the productivity of branched horizontal well in ribbon-shaped gas reservoir in the Sichuan-Chongqing region, according to the similarity principle between gas seepage and liquid seepage and the relationship between gas relative permeability and sulfur saturation summed up by Roberts, the famous Qi Chengwei's formulae are successfully generalized to pseudo three-dimensional productivity formulae of horizontal well in ribbon-shaped sour gas reservoir. On the basis of the revised formulae, the impact of sulfur deposition amount and permeability anisotropy coefficient on productivity is analyzed, and important knowledge that the effect of sulfur deposition amount on productivity is greater than that of permeability anisotropy coefficient is obtained and longitudinal bilateral horizontal well possesses more advantages than transverse horizontal well in ribbon-shaped sulphuric gas reservoir. At last, a proposal that the pseudo three-dimensional productivity formula derived by Qi Chengwei for radial branched horizontal well in circular petroleum reservoir should be promoted to sulphuric gas reservoir is put forward.