The invention discloses a device and method for preventing overloading of passengers in a bus. The device comprises an overloading detecting module, a control unit, an alarm and a wireless communication device. The overloading detecting module comprises a speed sensor, a plurality of pressure sensor and an infrared sensor which are connected to the control unit. The speed sensor is used for detecting the speed; the pressure sensors are arranged on bus seats and used for detecting whether the passengers are on the bus seats or not; and the infrared sensor is arranged in the bus and used for detecting whether the passengers are on the aisle area and the seats in the bus or not. The control unit comprises a decision module based on a processor; the alarm and the wireless communication deviceare connected with the control unit; the decision module is connected with an ECU of the bus; and the decision module judges whether the bus is overloaded or not based on sensor data of the overloading detecting module, and controls an engine of the bus to be stopped through the ECU of the bus under the condition that the overloading state is determined. The device and method have the advantage that overloading of the passengers in the bus is effectively prevented with the low cost.