Abstarct: Carbon nanotube is more amazing nanostructured materials as ever discovered. Unique properties such as high strength, light weight and excellent energy absorption capability makes this material just be of interest to scientists in making bullet proof vests. In this thesis, the structural model in ABAQUS software is used to analyze the mechanical behavior of carbon nanotube under ballistic impact. In this structural model a nonlinear connector is considered for modeling of stretching and torsional interactions, and a nonlinear spring is used for modeling of the angle variation interactions. The present model is constructed in the CAE environment of ABAQUS, So there is no need to programing for different loading and boundary conditions. Every feature of the software in the analysis of mechanical problems has to be imposed on carbon nanotube. In thi thesis impact is simulated by rigid body with specific mass as bullet. The effect of various parameters such as geometry, boundary conditions and type of carbon nanotube, the collision place and collision angle of bullet into the carbon nanotube has been studied on the mechanical behavior of carbon nanotube. The influence of different defects in the carbon nanotube has been investigated on it's energy absorption under impact too. Finally, given that at review of the mentioned parameters, geometry of bullet designed according to previous studies, by changing the geometry of the bullet, carbon nanotube behavior is investigated under impact. The results show that in the case where the nanotube was fixed at both ends absorbed energy when the bullet hit the middle of the carbon nanotube is maximum whereas in the case where one end was fixed at the relative height z=0.6 this value is maximum. The energy absorption of carbon nanotube decreases with the increase in bullet angle to the horizontal axis. In defective carbon nanotube; absorbed energy reduced that this decreasing in the Stone - Wales defect is more than vacancy defects.