In order to study the influence of structure parameters of the reinforcing rib to the mechanical properties of plastic well covers, according to the theory of elasticity, the stress situation of the plastic well cover with reinforcing rib is analyzed with finite element method. The load simulation of the plastic well cover with different reinforcing rib structure parameters is conducted with Abaqus software, and the relationship between the structure parameters of the reinforcing rib and the mechanical properties of the plastic well cover are analyzed. The simulation result shows the stiffness and mechanical properties of the plastic well cover are improved by increasing the height (h) or width (b) of the rib; if h is smaller than 80 mm, the effect of increasing h is extraordinary for improving the stiffness and mechanical properties of the plastic well cover, while the effect of increasing b is not obvious; as h increases, the effect of increasing h is declining, but the effect of increasing b is strengthening relatively; if h is bigger than 160 mm, the effect of increasing h is very small, while the effect of increasing b is higher than the effect of increasing h; the maximum stress of the reinforcing rib is higher than that of the panel, and their deference reduces as the mechanical properties of the plastic cover is improved.