BDS navigation system is widely used, and the message format is open and vulnerable to GNSS spoofing attacks. Navigation message authentication is an effective means to deal with spoofing attacks at the system level. Aiming at a B2a signal and combining it with China’s commercial cryptographic standards, this paper designs a message authentication scheme based on time-efficient stream loss-tolerant authentication (TESLA) and designs the B2a authentication message. By defining a new authentication message frame for broadcasting authentication messages, the broadcast content, broadcast sequence, and broadcast cycle are developed. The key indicators such as authentication error rate and time between authentications are analyzed by simulation test. The results show that the time between authentications is shorter and the message authentication efficiency is higher under the same security level as Galileo OSNMA service.