Abstract: The basic and non-basic N compounds in catalytic diesel were directly separated in this paper by acid-modified silica column and then quantified by gas chromatography-nitrogen chemiluminescence detection (GC-NCD) based on the established database obtained by following steps: firstly nitrogen compounds were extracted by neutral silica adsorption column, then the nitrogen compounds were concentrated and separated into basic and non-basic types using acid-modified silica column, and these two kinds of N compounds were finally analyzed by gas chromatography-mass spectrometer (GC-MS) to identify N compounds. Four kinds of catalytic diesels were tested. The results showed that the neutral nitrogen compounds including indole and carbazole in catalytic diesels oil occupied more than 90% (mass fraction) of the total nitrogen compounds. Catalytic diesel oils from different sources have different types and distributions of the neutral nitrogen compound. Basic nitrogen compounds, mainly including aniline, quinoline and benzoquinoline, occupied about 10% (mass fraction).