This paper presents a procedure for developing a finite element model of random chopped cotton fiber reinforced polyethylene composites to determine their mechanical properties. In experimental studies, composite plates with polymer (polyethylene) matrix and waste cotton fabrics reinforcements were manufactured in two different volume fractions (7.5% and 15%) by custom made extrusion technique. Some of the produced plates granulated down to the size enough to use in extrusion process and used again for plate production. These processes were repeated at most 6 times. Each processed material was subjected to uniaxial tensile experiments and stress-strain curves were obtained. In the finite elements analysis step, a unit cell model was developed and analyzed by ANSYS to obtain the effectiveness of reinforcements and fiber orientation, according to volume fraction. Finite element analysis results were compared to experimental test results and also effectiveness of fibers are investigated by the use of range of strain energy. It has been observed that by increasing the volume fraction of the reinforcement material, mechanical properties such as strength has been improved.