Abstract: Based on the dataset of observations of precipitation, visibility and winds since 1954 at the top of Huashan Mountain, the ratio between the precipitation at Huashan Mountain and at the nearby plain stations, which is defined as the orographic enhancement factor (Ro), and the relationship between Ro and visibility, were used to quantitively study the ways that air pollution aerosols suppress orographic precipitation. Ro decreased 14%－20% gradually during the measurement period, which means that the precipitation at the top of Huashan Mountain decreased 14%－20% compared with the precipitation at the plains stations. The indicated trend of Ro matched well with the decreasing visibility and increasing aerosol, which suggests that enhanced pollution aerosols suppress the orographic precipitation. The decreasing trend of Ro is mainly caused by days of the light and moderate rain (daily precipitation less than 30 mm), but not by days with precipitation more than 30 mm, which suggested that the thin short living orographic clouds are much more susceptible to precipitation suppression by air pollution aerosols. The precipitation less than 30 mm and 5 mm, respectively, can be affected by the aerosols entering the clouds for Huashan Mountain and Xi’an stations, which suggests that the more aerosols enter the clouds, the deeper precipitation clouds will be influenced by the aerosols to suppress the precipitation. In the spring and autumn when dynamical lifting plays the leading role, the suppression of aerosol to clouds at the mountain top is stronger than that in plains, and causes about 20% decrease with a maximum of 25% in precipitation at Huashan Mountain. In the summer for the thermodynamically driven clouds, the suppression of aerosol to the clouds at the mountain top and in plains is equivalent. The variations of Ro in different wind directions show that the decreasing trend of Ro increases with the wind speed, and the decrease of orographic precipitation exceeds 30% for 240－030 wind direction and wind speed greater than 5 m/s. The quantitative analyses of Ro and visibility show that Ro decreases from about 1.8 to 1.2 when the visibility changes from 14 to 8 km, and the decrement exceeds 30%. Ro at Huashan Mountain to Huayin stations is linearly correlated with the visibility, and the regression coefficient is 0.81. Finally, a brief physical model that aerosols suppress orographic precipitation is summarized based on the results.