Tidal flow is a periodic movement of unsteady and non-uniform,which has acceleration and deceleration process obviously,especially in coastal shallow waters.Many researches show that vertical distribution of tidal flow Reynolds stress deviated from linear distribution.The parabolic distribution of the tidal flow Reynolds stress was proposed by Song et al.(2009).Although the model fills better with field observations and indoor experimental data,it has the lower truncated series expansion of tidal flow Reynolds stress,and the description of the distribution is not very comprehensive By introducing the motion equation of tidal flow and improving the parabolic distribution established by Song et al.(2009),the cubic distribution of the tidal flow Reynolds stress is proposed.The cubic distribution is verified well by field data (Bowden and Fairbaim,1952; Bowden et al.,1959; Rippeth et al.,2002) and experimental data (Anwar and Atkins,1980),is consistent with the numerical model results of Kuo et al.(1996),and is compared with the parabolic distribution of the tidal flow Reynolds stress.It is shown that this cubic distribution is not only better than the parabolic distribution,but also can better reflect the basic features of Rcynolds stress deviating from linear distribution downward with the tidal flow acceleration and upward with the tidal flow deceleration,for the foundation of further study on the velocity profile of tidal flow.