Composite materials are a group of materials which have high strength and modulus and low density so their usage in industry instead of traditional materials like steel and aluminum have increased but these materials are susceptible to damages that are caused by impact. Low velocity impact on composite structures like beams can cause internal damages which can grow in further loading and cause sudden degradation of material strength. Flexural loads after impact is an example of these loads. In this thesis impact resistance and residual flexural strength of laminated glass polyester composite beams with channel sections were investigated. For this purpose some of the existing failure criteria for dynamic failure of composite materials were searched and among these criteria Hou criteria, Hashin criteria, maximum strain criteria and puck criteria were programmed and implemented in abaqus software. Simulation of impact and bending after impact showed that maximum strain criteria for fiber failure and hou criteria for matrix failure have the best accuracy for predicting the place and time of damage occurrence and residual flexural strength after low velocity impact. Low velocity impact tests were also done with different energies by varying the mass and height of the impactor and for this purpose 25 centimeter and 50 centimeter beams were used. After each impact test flexural test was done. In impact tests a kind of matrix failure were observed in the corner of the beam and exactly in the attachment of web and flange of the beam that was due to the delamination and strain concentration in this place and affected the residual strength after impact in high impact energies. For solving this problem cohesive element was used. Using this element for this kind of failure was an innovative method that was not used before in the literature review. Some of the results that were extracted from the thesis are as follows. Puck criteria for fiber failure showed to have low accuracy for predicting the damage in tension and compression in low velocity impact. Moreover in numerical simulations by fixing the impactor height and varying impactor mass three regions were observed in residual flexural strength and modulus after low velocity impact versus impact energy for 50 centimeter beam. The trend of these regions for residual flexural strength were all linear. linear region was also observed in the same diagram for 25 centimeter beam. Furthurmore by fixing the impactor mass and varying the impactor height three regions were observed. In the first region the matrix damage was low and its effect on residual strength of the beam was negligible. In the second region by propagating the matrix damage on the impact surface of the beam residual flexural strength was affected a lot so that this property lowered to the half of the intact flexural strength without prior damage. In the third region a plateau mode was observed that was due to the large amount of matrix damage on the impact surface of the beam that increasing the impact energy did not affect matrix damage severity a lot. Keywords: composite materials, channel section beam, low velocity impact, residual flexural strength