In this study, the transient nonlinear dynamic analysis of nanobeams reinforced with carbon nanotubes, which is under the lateral force, is investigated. The boundary conditions of the nanobeam are considered as clamped-clamped and the carbon nanotube is arranged in different distribution in the nanobeam. The differential equation governing for Euler Bernoulli beam using the Hamiltonian method is obtained.For this purpose, it is used of the couple stress theory and the Von Karman relationship between strain and displacement. Then, by using the semi-exact method and using the Galerkin’s method, the displacement derivatives are separated from the time derivatives and the equation derived is solved using Runge-Kutta's numerical method.To confirm the equation and its solution, a comparative study is performed that shows an appropriate fit between the results. Finally, the influence of parameters such as amount and time of applied force, size effect and type of nanotube distribution on the nonlinear frequency to linear frequency ratio and transient nanobeam dynamic response are investigated. A study is also conducted on the effect of the inclusion of nonlinear effects on the transient dynamic response when the nanobeam is under impulse load. The results show that the nonlinear vibrational frequency of the nanobeam with the FG-X carbon nanotube distribution is the highest and the FG-O carbon nanotubes distribution is the least.In addition, the FG-X distribution has the lowest nonlinear behavior and in the FG-Odistribution, the highest nonlinear behavior is observed.