Abstract: The method to humidify Fee catalyst is taken to simulate the change of properties of cohesive particles. The model presented in this paper is conformed by the measurement of the width of the static arching in hopper against negative pressure gradient. The effect of various factors, such as the unconfined yield strength of powder, the shape of a hopper , operation condition and the time of consolidation on the width of static arching is discussed in detail . The method to determine the minimal size of out - let of standpipe is presented. for the design of standpipe in industry.