Along　with　the　rapid　development　of　computer　technology　and　digital　image　processing,　traditional　PCB　technology　of　defect　detection　could　not　meet　the　demand　of　the　quality　of　PCB,　meanwhile　AOI　has　received　increasing　attention.　This　paper　mainly　introduces　the　AOI　machine　based　on　PCB　defect　detection,　hardware　structure　and　software　system　is　respectively　carried　on　the　design.　In　addition,　provide　a　new　method　of　defect　detection　which　is　based　on　the　comparison　of　contour　and　introduce　the　process　of　camera　calibration　chiefly.