Abstract: A coker diesel was distillated on the base of equal volume way to obtain fractions, which was analyzed to investigate the basic nitrogen content, mercaptan sulfur content and acid number of each fraction. The results show that the basic nitrogen content increases with the increase of boiling point, but the mercaptan sulfur is just opposite. The qualitative analysis of the coking diesel by GC-MS finds that the acidic substances are all phenolic compounds, and the boiling points of majority of phenol substances are less than 257 ℃. It is concluded that the majority of basic nitrogen compounds are concentrated in the higher boiling fraction, while the phenols and mercaptan sulfur compounds are in the low boiling point fractions.