The work aims to improve corrosion resistance of carbon steel Q235 organic coatings by adding silicon nitride (Si3N4) to epoxy resin as a kind of filler. Silicon nitride was uniformly distributed in epoxy resin in the method of ball milling. The protective effect of coatings with different silicon nitride content (on the basis of mass fraction) on Q235 carbon steel substrate was studied. Corrosion resistance of coatings with different silicon nitride content in 3.5% NaCl solution was characterized based upon electrochemical impedance spectroscopy (EIS), water absorption experiment, adhesion experiment and salt spray test. Low frequency impedance modulus and pull-off adhesion in dry-wet state of the coatings were improved by adding silicon nitride. At the same time, the addition of silicon nitride reduced water absorption of and improved salt spray resisting time of the coatings. Initially (0.5 h), low frequency impedance modulus of the epoxy resin coating (0% silicon nitride) was 7.7×108 Ω?cm2. The low frequency impedance modulus increased by two orders of magnitude after the addition of silicon nitride, but that of 5% coating was the maximum, 8.6×1010 Ω?cm2. With the extension of immersion time, low frequency impedance modulus of the coatings decreased inordinately, and that of the 5% coating was the minimum. After 2400 h immersion, low-frequency impedance modulus of the 5% coating was the maximum, 3.3×108 Ω?cm2. In conclusion, the addition of silicon nitride filler can improve corrosion resistance of the coatings, and protect the metallic substrate against corrosion to certain extent. When the silicon nitride content is 5%, the coatings exhibit the best corrosion resistance.