The air humidity data measured at 8 different-altitude observatories on the east and west slopes in the northern part of the Ailao mountains are used as a basis for studying the annual variation of the air humidity resource, the air humidity difference between the east and west slopes and the vertical distribution characteristics of the air humidity. The findings show that:(a) the maximum humidity occurs in July and the minimum humidity occurs in February-March,(b)the humidity resource on the west slope is better than that on the east slope and in dry season, the humidity increase effect on the west slope is particularly remarkable,(c) the water vapor pressure decreases with the altitude, and (d) the relative humidity increases with the altitude only in rainy season, but in dry season this correlation is very poor.