In this paper,the reach from the upper Luoqi to the lower Luoqi in the Fuling-Luoqi waterway is the research area.An unstructured triangular mesh hydrodynamic model is established on the measured topographic map of 1:1 000 scale,which is based on the method of volumetric method used to solve the two-dimensional hydrodynamic equation,to study the trend of the calculation results of the model in the multi-group relative grid ratio.It is found that the effect of the relative grid ratio on the calculation results of the calculation points in the flood is much greater than that on the calculation points in the river valley.When the relative mesh ratio is less than 1,the calculation results of the hydrodynamic model in the river have changed little,especially the average relative deviation of the river channel is close to zero.When the relative grid ratio is greater than 1,the average relative deviation of the model calculation results gradually increases.And when the relative grid ratio is large enough to stabilize,the average relative deviation of the calculated results in the flood area is larger than that of the river channel.With the increase of the relative mesh ratio,the average relative deviation of the calculation results of the hydrodynamic model in different water depth areas is different.