The invention relates to a SaaS-based identity authentication method, comprising the following steps: analyzing an identity authentication request which is acquired through a standard Portal protocol and sent by each user while accessing to a portal site, thereby obtaining a network parameter of the user; according to the network parameter of the user, acquiring account information bound with a user terminal device; sending the account information to a billing system, and acquiring authority information of the user from the billing system; if the authority information is an authorized state, judging that identity authentication of the user is successful, and returning back notification information of success of authentication to the user. By the technical scheme, the method provided by the invention realizes unified authentication for multiple identity authentication requests from different network authentication devices, solves a technical problem of incompatibility between different identity authentication systems and different network authentication devices, improves efficiency of identity authentication, and reduces cost of identity authentication.