Based on the granularity analyses of 376 samples from two typical profiles on high alluvial flat and 2005's flood sediment of the Weihe River in Weinan,Shaanxi, combining historical literature information, the flood recorded on sediment layers of high alluvial flat were researched. The results indicate that flood sediment on high alluvial flat of the Weihe River is mainly silt and very fine sand, stratified obviously and differentiated clearly , which can indicate the flood frequency, the flood level and the flood power. The two profiles, with the depth of about 5.3 m, are divided into 19 layers, which indicates that there were 19 floods of larger scale at least. The 19 floods determined by granularity analyses are basically consistent with that recorded on historical literatures. The granularity parameters such as Md， Mz， ó， Sk， Kg differentiate obviously, which indicates the differences of each flood. The flood depth on the high alluvial flat is higher than 1.6m of 2005, when the 15th， 14th， 10th， 3rd， 12th， 4th， 13th， 6th， 8th， 2nd flood occurred. The depth of these floods above the riverbed are larger than 8.1m, and others are near to or less than 8.1m，which indicates there occurred large or medium scale floods at that time. Based on the yearly precipitation when the modern flood occurred in the Weihe valley, it is determined that the most floods of WN1and WN2 profiles are caused by the obvious increase of precipitation at that time.