The flood characteristics of detention basin have been changed，with the increase of accumulative land subsidence. In this paper, basing on the analysis of land subsidence, a 2-D hydrodynamic model was constructed at the Jiakouwa Detention Basin using two different DEM datas. Then this model was used to simulate the flood routing processes under the scenario of 100-year design flood. The flood routing processes, inundated level, and inundated area before and after land subsidence were compared, the results show that land subsidence in Jiakouwa Detention Basin could slow down the flood routing process, decrease the inundated level, but increase the maximum inundated area under the same inflow. The conclusion can provide reference for flood control operation and disaster reduction in the Daqing River Basin.