For the communication waste of the exchange key establishment process in Local Area Network (LAN) security association scheme based on pre-shared key, an improved LAN security association scheme was proposed. A pairwise key between a new added switch and the authentication server was generated by improving the authentication and unicast key agreement process based on pre-shared key, and was used to the exchange key agreement processes between the new added switch and other nonadjacent switches. Then, on basis of the above improved scheme, a LAN security association scheme in trusted computing environment was put forward. In the improved authentication and unicast key negotiation process based on pre-shared key, the platform authentication of the terminal device was further increased, thereby realizing the trusted network access of the terminal device, and effectively enhancing the security of the LAN. Finally, the two LAN security association schemes were proved secure in the Strand Space Model (SSM). The results of performance comparison analysis show that the improved scheme reduces the number of exchanged messages and computation complexity of the exchange key agreement processes.