Abstract: Fibroblast activation protein (FAP) exists in tumor stromal fibroblasts and is a significant target for tumor diagnosis and treatment recently. Among the radioactive FAP-targeted tumor imaging agents, small-molecule tracers have received the most extensive attention. This paper elucidates the core structure of FAP-targeted small molecule drugs, categorizes the various design approaches employed for the development of novel small molecule imaging agents targeting FAP, up until December 2023. Additionally, a comprehensive analysis of FAP-targeted PET imaging agents and SPECT imaging agents with excellent biological performance or innovative structure is conducted. The structures and design concepts of these agents are carefully examined and summarized, with the aim of making valuable contributions to clinical diagnosis and treatment.