Abstract: In order to find out the operation and maintenance status of chemical instrument in thermal power plant, and improve the accuracy of on-line chemical instruments and the technical level of chemical supervision. The field investigation is carried out on the management model of online chemical instruments, the skill level of maintenance personnel and the comparison of qualification rates before and after correction of on-line chemical instruments in 18 power plants of China Huadian Corporation, the corresponding management and maintenance suggestions are given against the problems found in the investigation. In conclusion, the on-line chemical instruments have the problem of low measurement accuracy and they can not meet the requirements of operation control and chemical supervision.

Key words: on-line chemical instruments, maintenance, present situation, chemical supervision