Based on the model of non-uniform packing structure of powder mass, ultimate tensile strength of cohesive powder was evaluated by the cohesive force in the closest packing portion of the mass. As the cohesive tensile strength is given as the product of the number of particles, the co-ordination number of particle and the cohesive force between particles, it increases with moisture content and with decreasing void fraction. Experiments by means of our direct-tensiletest device verified the present analysis.