Objective To set up the life prediction model of the coating based on the grey theory and use the model to calculate the coating life of the solvent-free coal tar epoxy coating with different thicknesses in coastal chloride salt soil simulation. Methods By electrochemical methods, the electrochemical impedance spectroscopy of carbon steel with the solvent-free coal tar epoxy coating of different thicknesses in the simulated solution of coastal chloride salt soil was obtained. Based on the GM(1,1) model of grey theory and the relationship between the low frequency impedance modulus value and the immersion time, the prediction model of the impedance modulus at the low frequency for the coating was established in the simulated solution of coastal chloride salt soil. Results The low-frequency impedance modulus value still remained above 8. 3×108 Ω·cm2 , when the coatings with three different thicknesses were immersed in corrosive solution for 240 d. Applying the prediction calculation formula, the relative error was less than 6. 0% between measured and predicted modulus values of low-frequency impedance of the three kinds of coating in the simulation solution of coastal chlorine saline soil, C<0. 35, P = 1, and the prediction accuracy of the model was good. The life prediction of the solvent-free coal tar epoxy coating with the thickness of 200 μm in coastal chloride salt soil simulation was 781 days, and the coating was changed from the initial stage of immersion into the middle stage. With the increase of coating thickness, the coating life was longer, and the predicted life reached 2926 days when the coating thickness was 600 μm. Conclusion The corrosion model for life prediction showed good fitting precision and prediction reliability.