The atmospheric qualities of Olympic national stadium were measured by using the fine particulate meter (FPM),tapered element oscillating microbalance (TEOM,with a PM10 cutting head),visibility sensor and meteorological analyzer during Beijing 2008 Olympic games from 8 to 24 August,2008. The variation trend of diurnal average of particle number concentration showed that the nucleation mode (5-20 nm) was closely related to the nucleation process,and the concentration curve was unimodal. Atiken mode (20-100 nm),with curve of three peak values,was stronger influenced by human activities and growing process of nucleation mode. Accumulation mode,with a tiny trend for its diurnal average particle number concentration,was strongly affected by the weather conditions such as rain. The visibility,the particle number size distribution in rainy,haze and sunny weather conditions were also summarized. The conclusion that scavenging action of rain to the particles had close relation with particle size,and lower visibility in haze day was caused by the scattering excitation of accumulated mode particulate. Mass concentration of PM10 was calculated using the data of particle number concentration,and it showed a good coincidence with PM10 directly measured by TEOM. The correlation coefficient could achieve 86.1%.