Abstract: Perforation has greater impact on casing in oil field production. Casing failure mainly happened in the oil production strata. We established the cement sheath casing perforation model, analyzed the stress of casing after perforation and the result showed perforation was the main reason of casing failure. The greatest stress is on the aperture of the perforation casing. Cement sheath can reduce the casing stress. Under even load, the rising pressure on the cement sheath can make casing stress raise, which changes greatly as the type of casing varies, The bigger aperture can produce bigger stress. Under uneven load, the collapsing strength decrease obviously, so if the uneven load is very big, we'd best choose P110 casing to enhance the collapsing strength.