With the rapid development and deployments of the Internet of Things (IoT) technology, the demands of IoT applications have changed from the connections of the ubiquitous passive objects to the fusion among “human-computer-objects”. As one of the key technologies in IoT, radio frequency identification (RFID) becomes one significant intermediary of battery-less sensing, due to the lightweight, labelling, and easy deployment of the RFID tags. In order to understand the research progress and methods, this study focuses on the battery-less sensing research based on RFID technology. Particularly, this paper describes and analyzes the research work on four aspects: signal sources, sensing modes, sensing targets, and application scenarios, according to the working flow of sensing research. This paper introduces the research progress in RFID-based sensing from these four aspects, and also discusses the advantages and disadvantages of different technologies among the four aspects. Finally, the existing research is summarized and promising directions are presented for future research.