Abstract: According to the value of geometrical structure parameters and determined geometrical structure size of representative volume element (RVE) model of the fiber tow composites, finite element software MSC.Patran/Nastran as a platform to establish RVE finite element models of fiber tow composite and corresponding manufacturing defects were also implemented into the models. Grid element deletion method was utilized to implement all types of manufacturing defects. When crack-like manufacturing defects implemented into the RVE models, the crack width was obtained by moving the two opposite surfaces of the elements at the both sides of offset crack. The real morphologies of void-like manufacturing defects should be simulated as much as possible. According to material property parameter definitions of mechanics of composites and basic theories of micro-mechanics, the finite element computational micro-mechanics (FECM) methods to predict effective elastic properties and effective thermal expansion properties of composites were derived. Based on FECM methods, elastic constants and effective thermal expansion coefficients without manufacturing defects, containing a single manufacturing defect and containing all types of manufacturing defects were respectively predicted. The results show that the presence of all manufacturing defects will reduce elastic modulus and shear modulus, while Poisson's ratios and coefficients of thermal expansions may increase or decrease. Through comparison with the experimental test results, numerical prediction results are generally a little larger than experiment test results, but the overall effect is ideal. Wherein, the maximum relative error is 6.04%.