The utility model discloses a compatibility and maintainability-improved vehicle-mounted apparatus. The compatibility and maintainability-improved vehicle-mounted apparatus is divided into a host machine and a junction box; the host machine is connected with the junction box through a pair of rectangular aviation connectors; each rectangular aviation connector comprises a multi-core rectangular aviation plug and a rectangular aviation socket matched with the multi-core rectangular aviation plug, wherein the multi-core rectangular aviation plug is installed on a rear panel of the host machine; interface signals of the apparatus which are required to be lead out are connected with the aviation plugs; the rectangular aviation sockets which are matched with the rectangular aviation plugs are installed on the junction box; and inner signals of the junction box are respectively connected with various communication interfaces according to signal types. With the apparatus provided by the utility model adopted, operation steps for replacing the vehicle-mounted apparatus can be decreased, and operation time can be saved, and the compatibility and maintainability of the apparatus can be improved.