According to the corrosion development of rebar that occurred before concrete cover cracking under natural conditions, the corrosion layer was simplified as a non-uniform distribution with semi-elliptical shape to model the non-uniform corrosion of rebar. Formulas were obtained to calculate the corrosion expansion stress of the concrete cover by using theoretical analysis, and its accuracy was verified by compared with finite element results. According to the theoretical solution, the maximum circumferential stress is on the horizontal axis, so the development of the corrosion layer can induce the horizontal internal crack inside the cover. Increasing rebar diameter can effectively decrease the corrosion-expansion stress and improve the ability of anti-rust crack of reinforced concrete structure. Calculated results indicate that the critical thickness of corrosion layer in the uniform corrosion model is far less than that in the non-uniform corrosion model and the result of uniform corrosion model is conservative. Therefore, the non-uniform corrosion model is validated to be much closer to the truth to analysis the corrosion problems.