Abstract: Formal verification is in effect to detect security protocols. The development of BAN-like logics promotes the research of this area. At the same time, there are many problems with current BAN-like logics. Based on analyzing these BAN-like logics, a new formal verification method of security protocols is presented. The new logic can realize verification function of current BAN-like logics, and makes the verification process implement conveniently. Consequently verification can be realized automatically. This logic gives a new approach to the formal verification of security protocols.