Abstract: A method for protecting Register Transfer Level (RTL) Intellectual Property (IP) core is provided, which converts an original RTL IP core to a target RTL IP core embedded with protection measures. The method includes: Step S1, constructing a state machine whose mode is controllable against the original RTL IP core, the state machine has a normal mode appeared corresponding to the normal function of the IP core after the entry of a correct preset secret key value and a fuzzy mode appeared corresponding to the abnormal function of the IP core after the entry of wrong secret key value; Step S2, revise the data flow of the RTL code in the original RTL IP core to obtain the fuzzy RTL code of the IP core; and Step S3: combine the state machine and the fuzzy RTL code into the targeted RTL IP core. By combining the secret key control and fuzzy data flow, the being embezzled and reverse-engineered of RTL IP core can be effectively prevented.