Provided is a single-image-based fully automatic three-dimensional (3D) hair modeling method. The method mainly includes four steps: generation of hair image training data, hair segmentation and growth direction estimation based on a hierarchical depth neural network, generation and organization of 3D hair exemplars, and data-driven 3D hair modeling. The method can automatically and robustly generate a complete high quality 3D model of which the quality reaches the level of the currently most advanced user interaction-based technology. The method can be used in a series of applications, such as hair style editing in portrait images, browsing of hair style spaces, and searching for Internet images of similar hair styles.