Aiming at the forecast of big-flood in the Yangtze River Basin,while taking enhancing the reliability of the forecast and reducing the misforecast as the study objective,the relevant predictions are made with ternary and pentanary commensurability models in accordance with the method of commensurability theory under the comprehensive consideration of astronomical factors, climate characteristics,natural geographic feature,etc. on the basis of long-term historical big-flood data in the Yangtze River Basin,and then a mutual verification is made on the achievements concerned. Furthermore,combined with the laws of the activities of the astronomical factors of sunspot,lunar declination angle,etc. ,the relevant analysis and demonstration are carried out for predicting the future flood years,continuities,distribution areas and flood magnitudes,while the years of similar flood are given out as well. The result of the comprehensive forecast is as the follows: ( 1) it is predicted that big-flood is to occur along the mid-lower reach of the Yangtze River along with Ganjiang River flood,flood in the West Hubei,floods in Hubei and Anhui along the mid-lower reach of the Yangtze River,moreover,the flood risk is higher in the Jiujiang Section in 2018,while it is predicted that big-flood is to occur from the Yangtze River with the higher flood probabilities of both the mid-lower reach of the Yangtze River and Taihu Basin; ( 2) it is predicted that the flow-rate at Datong Station of the Lower Yangtze River is to be 72 000 m~3 / s in 2018 and its similar year is 1999,while it is predicted that the flow-rate at Datong Station of the Lower Yangtze River is to be 72 000 m~3 /s in 2019 and its similar year is 1995. The study result can provide a feasible method for analyzing the hydrological regime of the Yangtze River Basin and predicting the big-flood to occur therein.