The new power system puts forward higher requirements for the communication interconnection of power equipment, especially in power areas that are difficult to cover by public networks and private power networks. As an efficient means, although building power communication ad hoc network has the advantages of low cost and flexibility, it puts forward higher requirements for the security of power ad hoc networks. This paper proposes a lightweight and secure access method for power WIFI to better meet the real-time requirements of power ad hoc networks. Based on the analysis of STA and AP flexible networking switching modes of WIFI ad hoc network system, this paper focuses on the security challenges of power WIFI ad hoc network system. Meanwhile, according to the environmental characteristics of the power ad hoc network, we simplify and improve the classic WIFI secure communication in three stages: Scanning, link authentication, and association, to improve lightweight and secure access to power WIFI. The secure access example of power ad hoc network of multiple nodes proves the effectiveness of the proposed method.