Abstract: Special image sensor based on ordinary industrial CCD camera is developed to detect pool images during CO₂ short circuiting arc welding at real time. The compact mechanical structure and particular optical unit with semi-pentagon prism are introduced.Control procedure of pool image deletion is designed, which could eliminate the conflict between shooting schedule of the CCD camera and random occurrences of short circuiting arc and the operating principle of the image sensing system is illustrated in detail. Experiments show that clear pool images can be acquired from different sides around welding torch fast and correctly with the developed image sensor.