Based on the observations of precipitation and visibility ranges from 1961 to 2005 at the top of the Wutai Mountain, the ratios between the precipitation amount at Wutai Mountain and at the nearby plain stations (Yuanping and Yangquan), together with the relation between visibility and aerosol concentration were analyzed to reveal the effect of aerosols on orographic precipitation. Over the Wutai Mountain region, visibility, together with precipitation and number of wet days have a significant decline. Precipitation amount and number of wet days at Wutaishan Station, which are much larger than those the plain stations. Further, the ratios of precipitation amount, and numbers of wet days and the days with precipitation less than 5 mm between Wutaishan Station and the contrast stations also have a significant decline, which has a significant correlation (p<0.05) with visibility. It can be speculated that declining visibility indicates enhancing aerosol concentration, which possibly suppresses orographic precipitation. Decreasing orographic precipitation results in declining water resources in mountain regions; if no precipitation gauges at the top of peaks, the precipitation monitoring network can not capture the effect of declining orographic rainfall on areal precipitation, which leads to an underestimation of the decrease in areal precipitation, as well as water resources.