Abstract: Sand production and fracture closure will by caused by the unreasonable production of low permeability after fracturing.So the production of low permeability will not increase.This paper based on considering all the factors of sanding and applying the method of particle dynamics,establishes the critical gas flow velocity formula.The propping sand in the fracture will not be damaged if the output of gas well is less than the critical output,making the fracturing be available for a long time.In addition,the factors that influence the production of fractured gas wells are determined,such as the fracture width,fracture height,propping sand diameter,propping sand density,and gas density.It also researches the method to determine the largest output for keeping fracture flow capacity,laying a solid foundation for the reasonable production of gas field.According to the analysis of a well in cp gas field,it proves that the formula established above is reasonable.