The invention provides a network-based user identity information protection system. A user uploads identity information to a network identity management platform, and the network identity management platform generates a parent network identity card on the basis of confirming that all information is true and effective; when the user performs account number, a network service provider submits a network identity card verification application to the network identity management platform, and the network identity management platform generates a unique child network identity card through the parent network identity card provided by the user and transmits the child network identity card to the network service provider. According to the network-based user identity information protection system provided by the invention, different network identity cards are provided for each network service provider to isolate the relevance of user information between different service providers and reduce the situation that a network operator collect multiple pieces of user information of the same person in multiple different service types to analyze the privacy of the user; and by using the network identity card online and hiding the key information of determining the identity, the online and offline contacts are isolated, and the loss caused by network information leakage is reduced.