Abstract: A multiple random scattering ray-tracing model is developed for predicting the distribution of sound pressure levels in a three dimensional space of any kinds of rooms. This model considers the reflection and absorption on the surface of each wall and the scattering caused by the objects distributed randomly in the room. The objects therein like machines, furniture, etc. are regarded as obstacles which scatter the sound, so that the sound propagation is shown as a multiple scattering process. Thus the sound pressure level distribution in a diffuse sound field can be calculated more precisely.