The present invention discloses a method for determining encryption algorithm used in security communication based on Mobile Country Code (MCC) number. In this method, a Mobile Country Code (MCC) number list is preset in a Core Network (CN), and all the MCC numbers of those countries or service providers adopting the same self-developed encryption algorithms as those adopted by the homeland are stored in this MCC number list. When a User Equipment (UE) is calling or being called, the UE sends an International Mobile Subscriber Identifier (IMSI) information of the current subscriber to the CN, and the CN parses the information and extracts the MCC number after receiving the IMSI information. The CN compares the extracted MCC number of the current subscriber with elements of the MCC number list one by one, if the MCC number of the current subscriber is identical with a certain MCC number in the MCC number list, the CN selects the domestic self-developed encryption algorithm; if the MCC number of the current subscriber is not identical with any MCC number in the MCC number list, the CN selects an available standard encryption algorithm for the security communication. The CN sends the UEA of the selected encryption algorithm to an access network; then the access network sends the UEA of the selected encryption algorithm to the UE. The present method not only allows the coexistence of standard encryption algorithms and self-developed encryption algorithm, but also simplifies the process of encryption algorithm selection. Accordingly, the subscriber interest and service quality is guaranteed.