9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and its derivatives have garnered significant attention in the realm of flame retardancy treatments for epoxy resins due to their abundant P—H bonds and gas-phase flame retardant properties. However, the addition of DOPO can adversely affect the mechanical strength and other properties of the materials. With the increasing demand for a balance between flame retardancy and overall performance of epoxy resins in modern society, the construction of composite systems is beneficial for maintaining the overall performance indicators of the materials. Here, this article provided a comprehensive overview of the research advancements in DOPO-based derivative synergistic flame retardants for epoxy resins over the past five years, particularly focusing on the effective components such as DOPO-N, DOPO-P, DOPO-S, DOPO-Si, DOPO-C, and DOPO-bio-based materials. The flame retardant performance and mechanical performance indicators of the modified composite materials were discussed in detail. Although a large number of DOPO derivatives have been designed for flame retardancy in epoxy resins, there are still a few concerns that need to be addressed, such as complex production processes, unclear flame retardant mechanisms, and incomplete environmental safety assessment systems. The trend of DOPO derivatives is to use chemical structure modification techniques to impart better environmental and economic properties to epoxy resins with smaller loading amounts.