Abstract: Studied is the relationship between the wall wear amount of the casing and its collapse resistance by means of the vertical collapse and hydrostatic explosion system. Nine pieces of the Φ139.7 mm×7.72 mm P110 sample pipes with external surface wears are measured and tested in terms of dimensions like OD and WT，residual stress，yield strength， tensile strength and elongation，etc. Then the extreme collapse resistance test is conducted piece by piece to the said pipes to analyze the influences by wears of different degrees on the collapse resistance of the casing. The research result shows that once the wear degree of the casing reaches a certain critical value，its collapse resistance obviously drops，and that the collapse point always presents in the area with the most serious wear.