Provided are a high mount stop lamp and a brake system for vehicles. The high mount stop lamp includes an LED light group, a power input interface, and a control circuit board. The power input interface integrates a communication protocol pin. The control circuit board includes a current limiting circuit, a flashing control circuit, and a main control unit. The flashing control circuit is connected to the current limiting circuit and the power input interface. The current limiting circuit is connected to the LED light group, and the main control unit is connected to the flashing control circuit and the communication protocol pin and configured to control the flashing control circuit to output a continuous constant current or high-frequency on/off constant current to the LED light group to drive the LED light group to switch between a constant light warning mode and a super flashing warning mode.