Abstract: In recent years, ultra supercritical units have become the main units in China's electric power industry. With the improvement of material grade of ultra supercritical units, stricter quality of water and steam which needs to be monitored continuously and accurately by on line chemical instruments is required for thermal equipment. In order to master the operation status of on line chemical instruments for ultra supercritical units, according to the relevant national and industrial standards, this paper conducted a investigation on the operation status of 16 ultra supercritical units in 8 power generation enterprises of a electric power company, and grasped the maintenance management status from three aspects: maintenance mode and personnel qualification, calibration standards and instruments, and maintenance system regulations; The present situation of measurement accuracy is mastered from three aspects of instrument equipment rate, operation rate and accuracy rate. Based on the analysis and discussion of the problems found in the investigation, the suggestions for the operation and maintenance of on line chemical instruments of ultra supercritical units and the improvement of chemical supervision and management level are provided.