In the present article, the frequency distribution function of velocities in turbulent flow is derived by the theory of random walk, on the asumption that the phases of elementary waves are at random and independent with each other. The normal distribution is obtained for the frequency of velocity fluctuations as the first approximation. The second approximation is also obtained. As the number of elementary waves increases, the distribution tends to the normal distribution asymptotically. The frequency distribution of the velocity has a modified form of the normal distribution.