This paper aims to determine the corrosion expansive pressure and its change rule, study the process of concrete cover cracking under corrosion expansive pressure, and improve the service life of concrete structure. Considering the concrete strain softening and concrete damage, finite element simulation and analysis of the process of concrete cracking caused by rebar corrosion and the distribution and variation of corrosion expansive pressure were carried out by changing the parameters such as cover thickness, diameter of steel bar, and concrete strength. Results show that the expansive pressure of uniform corroded steel bar was nonuniform, which was influenced by crack. The expansive pressure reached its peak before the crack penetrated the cover, then it decreased quickly, and finally remained stable. The influence of cover thickness c and bar diameter d on expansive pressure was linear, and parameters c and d could be described with a unified c/d value. Furthermore, the larger the c/d value was, the larger the expansive pressure and corrosion rate were, which means the concrete cover cracking was delayed. Finally, a simplified formula was proposed to estimate the maximum expansive pressure, and the validity and precision of the formula were validated by experimental data.