Aiming at the real-time requirement of relay protection device, a secure startup mechanism of multi-core asymmetric software was proposed based on a self-developed chip with two clusters and four cores of ARM Cortex-A53 processor, which could meet both the security requirements of embedded devices and the real-time requirements of relay protection device. The overall design idea, security hardware protection module and software architecture of the mechanism are described, and the security is analyzed in detail. Experiments show that the proposed scheme can be used as a trusted system to measure the integrity of embedded devices, so as to realize the secure startup of embedded devices.