Since many years ago, composite materials have been selected as a replacement for some metals such as Steel and Aluminum in many industries, due to their high strength to weight ratio, high corrosion resistance, and many other features. Composite beams are such products of composites that are being used in building constructions, roads, bridges, etc. . Impact is an important subject in composite materials. Because impact damage reduce their strength. One type of impact that may be applied to composite beams is axial impact, which very little work on it has been published. Investigating residual axial-buckling strength of beams after impact is so important, because by the sudden buckling instability of beams, the entire structure may become unstable and collapse. In this research, glass-polyester channel section beams made by pultrusion method, initially placed under axial impact and then residual axial-buckling strength of beams after impact has been measured. In order to investigate the effect of impact damage on the residual axial-buckling strength of beams, axial strength of undamaged beams has been also measured. Simulation of the problem has been done in the finite element software ABAQUS/Explicit and in order to investigate damage initiation, the four failure criteria of maximum stress, maximum strain, Hashin and Hou have been compared with each other. In addition to these failure criteria, which are simple and well known, instantaneous damage evolution law has been used. For modeling of damage and defining material behavior of orthotropic, user subroutine VUMAT is used. Experimental tests have been performed to validate numerical results and simulation with related tests have been done for various conditions. In this case the effect of weight and height of the impactor and also length of the beam have been considered. By comparing the results of simulation and experiment, it was concluded that for axial compression of undamaged beams, maximum stress, maximum strain and Hashin failure criteria have had the best prediction for force-displacement and buckling mode, while Hou failure criteria have predicted much damage in the beam and the results of this criteria have been cautiously. For compression after impact, maximum stress and Hashin failure criteria have had similar results and also consistent with the experimental results. Also, with the help of research undertaken in this thesis, this result has been achieved that depending on the type of material used and loading and boundry conditions, Appropriate failure criteria should be used to model damage and then by simulating with this failure criteria it would be simple to achieve results that would not be easy to get them through the test, for example buckling mode and damage mode shapes. Keywords Pultruded beam, axial impact, residual axial-buckling strength, FEM, VUMAT, experiment