The invention discloses a user authentication method and system. The method comprises the steps of: creating a user block chain; obtaining information data provided by a user; encrypting the hash value of the information data of the user by adopting a digital signature technology, and sending the encrypted hash value and the information data to a user block chain node; and, according to the information data and the hash value, judging whether the user is a user registered in the user block chain or not, and if so, completing identity authentication of the user. By means of the user authentication method and system disclosed by the invention, the purpose of ensuring security of the user information and relatively high authentication efficiency can be achieved.