In view of the extreme climate in high and cold region and the field work conditions of groundwater monitoring, an on-line monitoring system with strong adaptability to the environment is developed. The system is mainly composed of water level sensor, data transmission module and central station. With D size battery as power supply, the system is of convenient maintenance. A number of measures in terms of hardware and software are taken to reduce power consumption and improve the stability and reliability of monitoring instruments in low temperature. In field test, the system operates well in cold weather. Automatic collection and remote transmission are accomplished to improve the working efficiency.