Using the shooting technique, we investigate the existence of oscillatory travelling wave solution of viscous flood wave in a wide rectangular channel with constant inclination. We prove the existence and uniqueness of an oscillatory travelling wave solution when the parameters of the viscous coefficient, frictional coefficient, inclination and altitudinal ratio satisfy certain conditions. Owing to the difficulty of analytical calculation, Matlab is used to compute the value of altitudinal ratio, and the structure of oscillatory travelling wave solution is also discussed.