Abstract: Since traditional public cryptography is difficult to deploy on intelligent terminals with limited resources, the security communication of intelligent terminals becomes an urgent problem for hydropower plants. In this paper, a secure data transmission algorithm aided by the network watermark is proposed, where a lightweight authentication scheme is implemented. Firstly, the sender uses a watermark-based authentication algorithm to authenticate the accessing intelligent terminals, while the receiver extracts the network watermark through a watermark extraction algorithm. This not only verifies the legitimacy of the transmitter but also generates a communication session password. Secondly, a secure data transmission model based on bidirectional identity authentication is designed using the key generated by network watermarks, combined with domestic cryptographic technology SM4. The experimental results show that the proposed trusted intelligent terminal secure communication method can not only improve the security of data transmission by authenticating the identity of the intelligent terminal but also improve the efficiency of data encryption.