Through the identical deformation of the basic equation about the contracted water depth of parabolic shaped channel, we can obtain a non dimensional formula, which is a typical quartic equation with one unknown . According to this equation ' s solution, we can also obtain an analytical expression for calculating water depth about the contracted water depth of parabolic  shaped channel, it provides one kind of new solution for calculating the water depth about the contracted section of parabolic shaped channel. The analytical formula is short  cut and its result is correct, and can be widely used. It also overcomes the shortage of consulting graph list and trial computation methods widely used in the past time.