In modern society, ventilation is an important method for removing indoor particles. This study applies the parameter of attenuation index to analyse the effect of the removal of indoor particles in the two typical ventilation modes called ceiling exhaust and slit exhaust. Experiment was conducted in a chamber and riboflavin particles were used as the indoor particles source, instantaneous microbial detection (IMD) used to measure the particulate concentration. The results showed there was obvious concentration difference in the vertical distribution for the slit exhaust when indoor particles tended stable, and the smaller the particle size was, the more obvious the difference was. Air exchange rate (ACH) is an important factor affecting the indoor particle concentration distribution. In the process of indoor free settling (air exchange rate is 0 ACH), the sedimentation rate were 0.086 h(-1), 0.122 h(-1) and 0.173 h(-1) for the particles of 0.5-1.0 mu m, 1.0-3.0 and 3.0-5.0 mu m. When the air exchange rate increased to 2.5 ACH, the differences in the attenuation index is significant. There was also a significant linear relationship between air exchange rate and attenuation index. Furthermore, the effect of the slit exhaust mode on the removal of coarse particles is more remarkable as the increasing air exchange rate. (C) 2017 Elsevier B.V. All rights reserved.