Sanding is a common phenomena during gas production in S gas reservoir due to the loosen sandstone formation, furthermore, the rock inner cohesion will be weaken by the water produced from interbed water and edge water, as the result, sand production in-situ is enhanced. Drawdown controlling is the reasonable strategy to sand control. To calculate the critical drawdown, a new model, which is based on the theory and lab testing data analysis to the rock composition, physical and chemical mechanism, cohesion weaken by watering, is developed in this paper. In this model, rock cohesion is considered as a function of mud content and changing with water saturation, which is a typical performance in the loose sand gas reservoir. It is more reasonable and reliable to forecast the sanding critical drawdown by this new model compare with field sanding monitoring data.