The invention discloses an on-line furnace-shutdown-free low-nitrogen burner transformation method. CFD numerical simulation and a thermal test are used, and fuel grading type burners are designed. According to the optimal transformation scheme, a primary fuel gun and a secondary fuel gun of the burners, a central hole forming template with primary fuel gun and the secondary fuel gun positioning holes, and a central sealing plate are manufactured. On-line transformation is carried out on the burners in sequence, when one burner is transformed, only gas of the transformed burner is cut off to extinguish fire, and the rest of the burners normally run. Old round air grading type burners are transformed into the fuel grading type burners on the basis of original refractory bricks, and on-linefurnace-shutdown-free transformation is completed through the large-proportion fuel grading design so that emission of nitrogen oxides can be efficiently reduced and meet standard requirements, and the problem about low-nitrogen transformation of the heating furnace without shutdown overhaul conditions is solved. Meanwhile, the requirements of flame form, heat flux, flame stability, daily maintenance and the like can be met.