The effect of the size distribution of spheroidal particles on the packing structure at the cake surface is studied in cake filtrations. By analyzing the forces and torques exerted on the depositing particles, the migrations and packing structures of spheroidal particles with various size distributions are simulated. For the packing structures of particles with a normal size distribution, the distribution of the co-ordination number in the cake is asymmetric, and its mean value decreases slightly as the standard deviation increases. When the major to minor axis length ratio of the spheroidal particles, phi, increases, the distribution of the co-ordination number becomes more uniform, but the average value does not change significantly. The packing porosity decreases linearly with increasing standard deviation. For the Rosin-Rammler distribution, the packing porosity and the mean co-ordination number increase with increasing distribution constant. The packing porosity of spheroidal particles increases with the size distribution in the order uniform distribution > Rosin-Rammler distribution > normal distribution. The packing porosity increases with the value of phi for all types of size distribution. The simulated results are compared with the available random-packing data, and the packing densities simulated by this study are closer to the experimental data than those of previous simulations.