In order to accurately predict the particle size distribution (PSD) of coal particle bed comminution under different applied pressures, the tests of two kinds of coal with four size fractions under five different applied pressures were carried out by TAW-3000 hydraulic servo testing machine. The Gaudin-Schumann(G-S) distribution is extended by the fractal theory and the JK size-dependent breakage model is discussed. Two mathematical models for predicting PSD of crushing products in coal particle bed comminution are proposed. Results show that the relationship between the mass-specific energy and applied pressure is linear. Because of the protective effect of fine particles, the change of particle size modulus d0 in G-S distribution is not significant, while the distribution parameter α decreases logarithmically with the increase of mass-specific energy. With the decrease of size fraction, the crushability of coal particle bed decreases, and a master curve can be used to fit the comminution characteristics of coal particle bed with different size fractions. The extended G-S distribution model and the JK size-dependent breakage model have better fit the results of coal particle bed comminution. This research provides a useful reference for the mathematical modelling of coal particle bed comminution.