In order to improve the precision of BGA solder joints inspection, the cross-section images of BGA solder joints are analyzed based on the 3D X-ray technology. The BGA solder joints or the BGA ball and background is segmented. The features of BGA solder joints defects and decision rules are extracted. And then inspection algorithms in vertical and horizontal cross section are presented. The defects of short circuit, shift, lacking solder, void, warpage and broken circuit can be inspected by the proposed algorithm.