The invention relates to a waterproof protection device for a cable intermediate joint. The device comprises a receiver antenna, a sensor antenna, a passive humidity sensor, a waterproof protection box and an RFID receiver, wherein the receiver antenna is installed in the RFID receiver, the passive humidity sensor is fixed on the waterproof protection box by adopting the adhesive method and is used for detecting whether the water enters the waterproof protection box or not, the sensor antenna is arranged in the passive humidity sensor, the RFID receiver supplies power to the passive humidity sensor, and the passive humidity sensor and the RFID receiver carry out data transmission with each other through the sensor antenna and the receiver antenna respectively. The device is advantaged in that the water inlet condition of a cable is monitored in real time by detecting the humidity in the cable, and the water inlet condition in the cable can be found in time.