Abstract: To accurately put the De-NO_x system into normal operation during deep peak regulation of a 300 MW subcritical unit at low load, a wide-load De-NO_x technology was proposed by directly heating the flue gas with reheating device. Results show that this technology can greatly improve the flue gas temperature by 10-30 K at the inlet of selective catalytic reduction (SCR) system, which ensures a normal operation of the SCR system at low load during peak regulation process. On the other hand, during start-up process, the flue gas reheating burner can greatly shorten the operation time of the SCR, thus meeting the needs of grid connection and putting the SCR into normal operation.