Abstract: It is very import ant to calculating the flow resistance and to confirm the velocity distribution under ice cover or ice jam.Many researches have been made for many years to suppose the mean velocity of flow sections is equal to that of the ice cover area and that of the bed area,and the validity of such assumption is argued in this paper based on the Prandtal's semiempiristic turbulence theory and the formula of velocity of logarithm distribution.And it is also found that falsehood would be induced in calculating flow resistance in shallow rivers based on the assumption that the slope of energy in the ice cover area is equal to that in the bed area And the ways and means are proposed.