With the rapid development of modern transports, the increasing demand of intelligent sensing and information interaction requires vehicle to everything (V2X) communications. Vehicle could directly communicate with other vehicles or roadside unit (RSU) though the on board unit (OBU) under PC5 interface. This poses a serious challenge to the security mechanisms of existing communication systems. Secret key generation based on wireless channel is an emerging technology for communication network security. It exploits the reciprocity and time variability of wireless channels to generate symmetrical keys. This physical layer security key distribution method owns benefits of low complexity and high security, which is suitable for dynamic network in V2X systems. We propose to a Wiener filter-based method to enhance the reciprocity of wireless channel due to the vehicle movement, which can guarantee the success of secret key generation in LTE-V2X systems. We design a simulation system to verify the feasibility of the proposed methods and setup a test system based on vehicle and universal software radio peripheral (USRP) software defined radio platform. The effectiveness of our proposed method is verified in simulations and practical tests.