Since powder particles' dimension is very small, each powder particle is not in contact with neighboring ones in their packing system, Van der Waals force and electrostatic force could not be neglected. Moreover, powder particles in paste are separated by water; packing density of powder particles in paste could not be calculated by Stovall model, which has an assumption that particles are contiguously packed, that is the Stovall model is only for dry particle system. In this paper each detached powder particle in paste is imaged to be coated with a water film, and the particle together with water film coated around is viewed as compound particle, which is in contact with neighboring compound particles. Packing density of powder particles in paste system is transformed into packing density of compound particles in imaginary dry particle system. Developed from the Stovall model a method for calculating packing density of powder particles in paste with continuous particle size distribution is proposed in this paper, a new experiment technique and equipment are devised and validity of this method is verified by experiment. (C) 2008 Elsevier B.V. All rights reserved.