This paper focuses on the issues of the fibre-reinforced composite material microstructure and presents a new numerical method to generate random fibre distributions and predict the macroscopic mechanical properties of composite materials based on the represent volume element (RVE). The method, named the random sequence generation algorithm (RSGA), obtains fibre radius distributions and positional relationships by image processing to generate a statistical equivalence RVE effectively. On this basis, the composite material microstructure finite element model is established to predict its macroscopic elastic properties by Python language in ABAQUS. Comparative analysis shows the algorithm is in good agreement with experimental results and has the statistical equivalence herein. The research of this paper on the algorithm for composite materials of fibre distributions provides a useful alternative to generate random numerical models that can be used in micromechanical analysis of composite materials.