With the improvement of national standards for discharge of pollutants, the 150 mg/Nm³ emission of NOx from the cracking furnace of the ethylene plant in Yangzi cannot meet the requirement of no more than 100 mg/Nm³ stipulated in the new standard. The burner was modified while the process conditions remained the same. To solve the problem of over high NOx emission after modification, some measures such as daily adjustment and optimization, steam injection and valve sealing were taken to meet the NOx emission standard.