Abstract: A design method of automatic assembly defect detecting system based on industrial computer tomography technology was referred. For the realization of non-destructive detecting of assembly defects such as leak installing and wrongly installing in work piece internal structure, this system adopted C/S model, using C++ Builder as front-end development tool and using SQL Server 2000 as background database management system. First defect region was located fast and coarsely using gray levels of the reconstructed image. Then it was recognized accurately by using circle projection value, direction code value and Zernike moment value as character parameters. The system was put into use in ICT center of ChongQing University. Its recognition speed and precision satisfied users demands, and its working effects were favorable.