It is found that most of incipient velocity formulas’ incipient coefficient K is a variant by analyzing and comparing some existing incipient velocity formulas. This paper points out the reason why coefficient K is variable. Theoretical analysis indicates that the coefficient K should not be a constant even for uniform sediment, while K should vary with the change of incipient condition, which is why many kinds of incipient velocity formulas are not accurate enough. Flow depth, non uniformity, and shape of sediment, and the relativity between the size of sediment and flow depth are factors which influence incipient condition. A incipient velocity formula is put forward based on these factors, and agrees well with the field and experimental data. Through comparison,it is found that the formula is superior to Zhang Rui jin’s formula, Shamov’s formula and Zhang Qi wei’s formula.
