The invention provides a device for protecting a water tank and the pressure in an air cylinder of mixer. The device comprises a multi-way valve, a pressure sensor, a vehicle state acquisition unit, a controller and a reversing valve. The multi-way valve is installed at one end of the air cylinder of the mixer; the pressure sensor is used for acquiring pressure data of the air cylinder through the multi-way valve; the vehicle state acquisition unit is used for acquiring speed data of the mixer; the controller is used for receiving the pressure data and the vehicle state data, judging whether the mixer is in a static state or running state according to the vehicle state data, comparing the pressure data with a pressure threshold, and generating a control signal according to the comparison judgment result; the reversing valve is used for forming a loop of the air cylinder and the reversing valve when the mixer is in the running state, to stop pressurizing the water tank. The invention also provides the mixer. The water tank is not pressurized when the mixer is in the running state, thus air pressure in the air cylinder of a chassis can meet the braking pressure strength, so that the requirement for protecting the braking pressure of the air cylinder and the requirement for pressurizing and depressurizing of the water tank are met.