The invention provides a vehicle-mounted gateway controller and a working mode conversion method and a system thereof. The method comprises the following steps: under the normal working mode, the power supply modules of the vehicle-mounted gateway controller are separately supplied with power for the microprocessor, the communication module and the signal transmission module; upon receiving a sleep request, transitioning from the normal operation mode to a low power consumption operation mode to cause the power supply module to stop supplying power to the signal transmission module and periodically restore the power supply of the signal transmission module to detect whether the signal transmission module receives an external signal when awakening the signal transmission module; if so, switching from the low power operation mode to the normal operation mode. The vehicle-mounted gateway controller of the invention effectively saves power consumption and prolongs the effective power supply time of the battery by designing the mutual conversion between different working modes.