Abstract: According to some previous results,the relationships among three common incipient motion conditions are deduced.Considering these relationships,dozens of incipient motion conditions are united,and K of all kinds of formulas is otained commonly from 3.37 to 7.86.This result is helpful to select appropriate incipient equation.Based on this research,the comparison study is made between pebble factual data in outdoors flume of Hanqiwei in Minjiang,1965,and calculation results of parts of classic formulas.This result is also useful to select appropriate incipient equation in Dujiangyan,Minjiang.