For the corrosion defects of oil casing, the existing inspection techniques cannot achieve visual monitoring. In addition, due to the narrow space between the oil pipe and the casing, the traditional visual methods cannot be placed inside the space. A visual monitoring system for corrosion defects was proposed. First, a spherical reflector was utilized to bend the imaging optical path so that the visual hardware was placed along the longitudinal direction of the oil pipe and the monitoring of the oil pipe and casing can be realized simultaneously. In addition, a local texture mapping method was proposed herein to mitigate image distortion resulting from optical path bending. The local perspective transformation of the image restores the real features of the target to be detected and lays the foundation for subsequent feature recognition.