In order to improve furfural's solubility and selectivity in refining the coker gas oil, two kinds of assistants (A and B) were chosen in this test and used to investigate the effects on yield of the refined oil and removal rate of the basic nitrogen. Based on the industrial operation condition, we choose 60 degrees C as the extract ion temperature, and from the intermittent test in laboratory, the laboratorial result shows that the yield of refined oil increased considerably and the removal rate of the basic nitrogen enhanced greatly after adding the assistant A under the little rate of solvent/oil. When the ratio is 0.5, adding 4% of assistant into solvent, the yield of refined oil and the removal rate of the basic nitrogen increased by 3.86 and 9.10%,respectively. In contrast, the assistant B has good effects on that under the big ratio of solvent/oil, especially on th e ability of the removal of basic nitrogen compound.