Abstract: Based on the relative humidity index of agricultural drought and crop damage data, this paper analyzed the conventional observation data and crop yield data of six meteorological stations in Hefei from 1980 to 2009 and disclosed the temporal and spatial variation of drought in Hefei and the yield damage caused by drought. This paper also analyzed the relationship between the crop damage rate and the relative humidity index, and set up the criteria of drought risk related to the relative humidity index for the two typical crops: wheat and rice. The results showed that the relative humidity index of Hefei was normal or humid. It was more humid in the south than in the north, meanwhile, the surface humid index decreased by 0.048 per decade. The threshold value of different drought grades (mild, moderate and heavy drought) on the base of relative humidity index was from -2.0983 to -3.4281 for wheat, and from -0.9371 to -2.5660 for rice. In general, the wheat had more tolerance to drought than rice, so the rice had higher risk in drought.