In order to meet the requirement of information society, governments of all countries are trying to establish a security system that can be monitored to combat criminals engaged in illegal activities such as using communication encryption technology and computer technology to carry out secret communication, and inhibit rampant computer crime. With the large-scale application of cryptographic techniques, countries have adopted various forms of key escrow policy. Key escrow technology aims to provide new access to acquiring information to decrypt key in an emergency. It is used to save the user's private key backup, which can help national security departments to obtain the original plaintext information when necessary and can also recovery ciphertext when the users lost and damage their own key. Recently years, it has been one of the hottest subjects in cryptology circle to find out a compromise between the protections of user privacy and ensuring the right of government agencies to monitor. In this paper, several typical key escrow schemes have been studied, including escrowed encryption standard, key recovery technology, applications of key escrow in PKI, etc., and the research development of key escrow technology in recent years has been analyzed.