To improve denitride ratio in lubrication oil NMP refining for improving the stability of basic oil , the me thod of combing physical extraction and chemical reaction was applied , that is , adding additives to the NMP solvent refining process , letting the additiv es reacting with nitride to removing nitride compounds .This additive is appraised synthetically based on the rate of removing basic nitrogen, influence to the properties and yield of refined oil.The sing le stage and the simulating three stages experiments show that the NMP solvent refining with addition of assistant can remove basic nitrogen in distillate oil efficiently and raise the oxidation stability .The mass fraction of assistant has no remarkable effect on the yield of refined oil and its index of refraction.The optimum operation conditions for single stage refining are :solv ent to oil volumic ratio is 1.0, extraction temperature is 80 ℃, the mass fraction of assistant is 0 .7 %.Under these conditions, the yield of refined oil is 87 %, the index of refraction of 60 ℃ is 1.459 8 and the mass fraction of basic nitrogen is 67 μg/ g .The optimum operation conditions for simulating three stages refining are :solvent to oil volumic ratio is 0 .75, the mass fraction of assistant is 0 .5 % , extraction temperature is 80, 70 and 60 ℃ for top stage , middle stage and bottom stage , respectively .Under these conditions , the yield of refined oil is 88 %, the index of refraction o f 60 ℃ is 1.460 1 , andthe mass fraction of refined oil basic nitrogen is 57 μg/g .