Spectral radiative transfer between particles in a semitransparent medium (i.e., water, glass, and air) needs to be considered when photo-transmission or high-temperature phenomenon is involved. However, the particle size distribution during application is generally an un-continuous change and conventional simplified treatments of particle size distributions would induce large radiative transfer differences between the calculated results and experimental data. In this study, the differential-integration method is developed and put forward based on measured non-uniform particle size distribution couppled with Mie scattering codes by the authors to calculate the spectral radiative properties of non-uniform size particles, which can obtain higher calculation accuracy. The Monte Carlo ray tracing (MCRT) method is adopted to solve the radiative transfer equation (RTE) of a semitransparent medium with non-uniform size particles. The research results indicated that the maximum relative transmittance error between experimental data and calculated data can decrease from 53.1% to 3.8%, when the optical properties of the particles with non-uniform size distribution were calculated using the differential-integration method to replace convectional effective uniform size distribution. (C) 2018 Elsevier Ltd. All rights reserved.