The method of determining the mechanical properties of unidirectional fiber reinforced composites and laminates, as well as the method for determining the fatigue life of the blade spar of the helicopter, some details of which are made from composite materials are developed. Modeling techniques of composite material with different relative to the direction of the fibers, and a method for determining cycle fatigue are proposed. This method does not require averaging over the volume of the composite, and uses only surface “measurements”. Total matrix of elastic constants of various reinforced composites were found. The full-scale computer simulation of bench tests on the fatigue life of the specimen helicopter blades produced. It is found that the results of calculations identical with the experimental data. Keywords: finite element method, reinforced composites, mechanical properties, fatigue life.