Due to the simularity of the circulation situation， weather impact system and water vaportransportation lead to the synchronism of therainstorm processes in the river basins of Jinshajiang and Yalongjiang，and the combination of runoff yield and flow concentration in spatia-temporal movement， it is easy to form great flood in the mainstream and tributaries at the same time. The hydrological data of the Panzhihua andTongzilin stations from 1965 to 2014 were used to analyze the flood compositions and coincidence probabilities between the rivers of Jinshajiangand Yalongjiang. The results indicate that the great floods generally occur in the upper and middle reaches of Jinshajiang River and YalongjiangRiver from June to October， especially from July to September， during which the occurrence frequency of the maximum annual flood peakdischarge is over 95%. The floods are characterized of flat fluctuation，long duration and large water volume in the middle reaches of theJinshajiang River and the lower reaches of the Yalongjiang River. The floods can last about 15d， and flood peak coincidence probability is about50%. The probabilities of 3d， 7d and 15d flood process coincidence are respectively 30%， 36% and 52%. Based on the results of peak flood twodimensionalCopula joint distributions between the Panzhihua and Tongzilin station， great floods generally occur between the Jinshajiang Riverand Yalongjiang River.However， the probability of great floods in both two rivers is not high at the same time. If it happens a great flood in theJinshajiang River， there would be a higher probability for a large flood in the Yalong River.