Objective The electrochemical behavior of the solvent-free epoxy coal tar coating was investigated in the soil solution of saturated water content. Methods The solvent-free epoxy coal tar coating was applied on Q235 steel, the open circuit potential and electrochemical impedance spectroscopy of the coatings at different thicknesses and different buried time were tested, and the effects of coating thickness and buried time on the electrochemical behavior of the coating were explored. SEM analysis of the elemental composition of corrosion products on the substrate surface were used to explore whether the aggressive substances reached the substrate surface and was involved in the corrosion. Results The stable open circuit potential of Q235 steel with a coating thickness of 200 μm was about -0. 37 V, and the corrosion potential shifted positively by about 0. 28 V as compared to that of the Q235 bare steel. With the increase of coating thickness, the open circuit potential showed a rising tendency, the capacitance arc radius increased, and the shielded blocking ability of the coating in aggressive solutions was improved. The protective performance of the coating declined, the capacitance arc radius reduced and water absorption increased with the prolonging buried time in soil, but the low-frequency impedance modulus value still reached up to 8. 8×107 Ω·cm2 . The energy spectrum analysis showed that no corrosive substances such as Cl- appeared on the surface of Q235 steel. Conclusion The solvent-free coal tar epoxy coating in soil solution could effectively form a shielding layer and provided an effective protection for Q235 carbon steel.