Abstract: As one of the tasks of Mountain Flood Disaster Survey and Evaluation Project，this study，taking 117 small watersheds in Lichuan County in the west mountain regions of Hubei，calculated design flood of small watersheds by instantaneous unit hydrograph method. Based on the calculation result，the relationship between the small watershed area and design flood was analyzed. The case illustrated that there was a power function relationship between the small watershed area and the design flood，with the correlation exponent of regression equation over 0.99 and P-value of significance test less than 0.01 when the areas were less than or equal to 200 km². This study has reference significance for selection of design floods for small watersheds in the similar regions.