Palmer Drought Severity Index(PDSI) perhaps is one of the most widely used regional index of drought. Because of the sensitivity of the index to different areas, some problems come in some research work on the drought in Huaihe area using modified PDSI by others. Based on the conventional surface observations data from Kaifeng, Xinyang and Chaohu stations, a modification of Palmer Drought Severity Index, on the ground of the modifications in 2004, 2005 and 2008, in Huaihe area, is carried out to indicate the drought/wet more accurately. The subtropical monsoon climate in Huaihe area and Kansas, Iowa is a little different when some research work is carried out on climate drought/wetness using Palmer Drought Severity Index. The antecedent drought/wetness affects the next period differently, that means, the antecedent drought or wetness affects less in Huiahe area. Therefore, a parameter is added to improve the sensitivity. The result shows that the modified index makes a great improvement in reflecting the drought severity in Huaihe area.