Abstract: The influence of hydrotreating depth on the properties of diesel with low-sulfur and low-aromatic was investigated by simulating two-stage hydrotreating technology using two separate fixed-bed microreactors and different light cycle oils (LCO) feeds. The first reactor was packed with Ni-W sulfide catalyst, and the second reactor was packed with Pt-Pd noble metal catalyst. By adjusting the space velocity and reaction pressure, diesels with various hydrotreating depths were obtained. The results show that after deep hydrotreating, the density, refractive index, and the content of sulfur, nitrogen, and total aromatics decrease, while the hydrogen content and cetane number (CN) increase. The aromatic content of hydrotreated diesel is linearly related to the chemical hydrogen consumption, refractive index, density, and CN. The slope and intercept of the linear fitting of aromatic content and CN are different for various LCO, closely relating to the hydrocarbon compositions and the carbon number distributions. The intercept represents the CN of diesel after full aromatic saturation, and the slope reflects the contributions of aromatic saturation to CN. For feed LCO-I with 88 % of aromatic content, the CN will increase 0.26 units for every 1 percentage point reduction in aromatic content, and will reach up to 42.0 units after aromatic saturation in full. For the hybrid diesel LCO-II with 31% of aromatic content, every 1 percentage point reduction of aromatic content will increase the CN of 0.66 units.