The invention relates to a high-voltage DC transmission system earth electrode state monitoring device, which is characterized by comprising a microprocessor. The microprocessor is respectively connected with a digital temperature and humidity sensor, a digital water temperature sensor, a water level sensor, an antenna (1), a crystal oscillator and a battery. The high-voltage DC transmission system earth electrode state monitoring device has the beneficial effects that the persons, the time and the workload for operation and maintenance of the high-voltage DC transmission system earth electrode can be effectively reduced, the work intensity of first-line production persons is lessened, the work efficiency is improved, and the labor cost is saved; and due to the high-integration and simple design, the device has the advantages of good environmental adaptability, high safety reliability, and long-time maintenance free, and the mounting and the use are easy.