Orientation detection is not considerably performed for describing the microstructures of three-dimensional (3D) fibers. Therefore, a novel 3D fiber orientation detection method is proposed based on a facet model for converting the 3D fiber orientation detection into two-dimensional (2D) plane detection, reducing the computational complexity and realizing the accurate detection of different diameter fiber orientations. The size of the model window should be slightly larger than the fiber diameter for obtaining the optimal results. The experimental results denote that the proposed method is more accurate and fast when compared with the existing typical algorithms at obtaining the 3D fiber orientation data in case of different diameters.