Wireless power transfer (WPT) is a promising technology and has potential applications where the wired power transmission is inconvenient or impossible,such as wireless charging of sensors and power harvest of battery-free devices.In this paper,the research significance and working principle of the WPT are introduced.Then a research subject is put forward that the efficiency of the rectifier in the receiving terminal of the WPT system is sensitive to the input power.Subsequently,researches carried out to cope with this issue are discussed.Among them,three novel efficient methods are detailed in this paper,which use passive network to extend the input power range for high rectifying efficiency.Finally,the future research orientation of the microwave rectifier is discussed.