Abstract: In this paper, the sound pressure levels (SPLs) at 18 receiving points in an auditorium are obtained by the simulation using acoustic software ‘Odeon’. According to comparison of sound field uniformity, the effect of ray number on the directivity of the source is explored. It is shown that for the effect on directional source, a threshold of ray number exists:for less than 100 rays, the directivity of the source can be better revealed; for the ray number between 100 and 500, the directivity is vague; for more than 500 rays, the sound field has good uniformity, so the source is similar to an omnidirectional one.