The invention discloses a network identity authentication method and system. The network identity authentication method includes that a client side processes first time and first information, encrypts to form second information and sends the second information and a user identity to a server side; the server side receives the user identity and the second information, acquires the first time by decrypting the second information and performs preliminary authentication; after preliminary authentication is completed, the server side encrypts second time to acquire third information; the server side judges whether time difference of the first time and the second time is smaller than a preset value or not, if yes, authentication of the client side by the server side is successful, and the third information is sent to the client side; the client side decrypts the third information to acquire the second time; the client side calculates time difference of the first time and the second time, and if the time difference is smaller than the preset value, authentication of the server side by the client side is successful. By the network identity authentication method and system, preliminary authentication and bidirectional identity authentication of the client side and the server side are realized, and the problem of safe storing of a secret key is avoided.