VANET (Vehicular Ad-hoc Network) is the one mainly utilized to create communication networks for vehicles or other roadside devices so that they can quickly share and receive messages. Nevertheless, VANET belongs to the family of wireless networks, which means VANET functions are unsafe. In order to provide safe communication channels, we introduce the key agreements technology to VANET communication. Traditional key agreement schemes, however, are inefficient and would consume too much of the resources especially when they are handling large groups of users or when groups are to be combined. To improve the efficiency, we use the Chinese remainder theorem to build a batch key agreement protocol instead. The improved key for VANET environments is a safer and quicker way to establish communication channels.