Abstract: A secure boot method. The method may be performed by a communication device. According to the method, the communication device can flexibly perform secure boot by using different cryptographic algorithms based on different security requirements, to ensure security of the communication device. The communication device may obtain external secure boot code (ESBC). The ESBC includes a code segment of a first cryptographic algorithm. After the ESBC is obtained, the communication device may perform an integrity check on the ESBC, and after the integrity check on the ESBC succeeds, verify a signature of next-level software based on the first cryptographic algorithm. When a cryptographic algorithm used by the communication device cannot meet a security requirement, the ESBC may be obtained, and the first cryptographic algorithm included in the ESBC is used to perform the secure boot, to meet the security requirement.