The method to diagnosis inner wall defects by combining infrared technique and inverse heat conduction calculation with computerized axial technique is a challenging subject because of difficulty in mathematical theory and being confined by geometrical shape. The inner wall defects at corner of a 3D spheroid are located using this method in this paper. The general analytic equation of inner surface is given based on the exposed surfaces temperature data obtained by scanning, which is as an extra bounder condition in the inverse solution to find inner boundary geometry. The size and position of defects can be determined from that. The feasibility of the method is also proved. It is a diagnosing foundation for this kind of equipment and it can be applied to other situations when the second or the third conditions are prescribed along the inner boundary.