Abstract: Based on the relationship between the vertical turbulent dispersion coefficient and hydraulic geometric shape,the distribution of local water depth with transverse surface in straight channel is put forward. The distribution of transverse turbulent dispersion coefficient and it's expression of average value are determined. The cross-section averaged transverse turbulent dispersion coefficient is found to be in good agreement with the of experimental data of 138 sets. The transverse turbulent dispersion coefficient calculated by using the equation are close to the observed. It indicates that the equation is not only nxme reasonable and clear in terms of theory and mechanism but has also the lowest error than others.