Abstract: At present, the network time protocol (NTP) is the main time protocol used for time synchronization in wired networks. It can achieve a synchronization accuracy of more than ten milliseconds in wide area networks and a few milliseconds in local area networks. However, due to the openness of the protocol, there is no security protection. Under the circumstances, it is extremely vulnerable to network attacks, which brings potential risks to customers who need high security. The NTP protocol can increase security strategies to deal with possible security risks. The message digest algorithm 5 (MD5) and the secure hash algorithm (SHA-1) message digest algorithm is introduced into the NTP protocol algorithm, which is effective to verify data integrity and prevent data packets from being tampered with to ensure the security of time synchronization. Further, for these two types of algorithms, Hash encryption of key data frames of NTP packets is proposed, which can further improve the security of time synchronization while maintaining good synchronization accuracy. Experiments have compared the influence of the synchronization effect brought by the addition of the algorithm. The results show that after the message digest algorithm is added, NTP can still maintain millisecond-level synchronization performance, which is of great significance to the realization of the NTP secure time synchronization method.