Image and video synthesis has become a blooming topic in computer vision and machine learning communities along with the developments of deep generative models, due to its great academic and application value. Many researchers have been devoted to synthesizing high-fidelity human images as one of the most commonly seen object categories in daily lives, where a large number of studies are performed based on various models, task settings, and applications. Thus, it is necessary to give a comprehensive overview on these variant methods on human image generation. In this article, we divide human image generation techniques into three paradigms, i.e., data-driven methods, knowledge-guided methods, and hybrid methods. For each paradigm, the most representative models and the corresponding variants are presented, where the advantages and characteristics of different methods are summarized in terms of model architectures. The main public human image datasets and evaluation metrics in the literature are also summarized. Furthermore, due to the wide application potential, the typical downstream usages of synthesized human images are covered. Finally, the challenges and potential opportunities of human image generation are discussed to shed light on future research.