In　this　paper,　ultrasonic　C-scan　imagery　technique　is　applied　to　measure　the　nugget　diameter　and　image　the　defects　in　a　spot　weld　of　a　high　strength　galvanized　steel　sheet.　In　order　to　enhance　the　test　precision,　the　ultrasonic　C-scan　image　is　divided　into　six　characteristic　color　regions　and　the　related　A-scan　signals　are　analyzed　according　to　the　structural　characteristics　of　the　high　strength　galvanized　steel　spot　weld.　The　results　indicate　that　the　nugget　diameter　can　be　measured　accurately,　and　the　shape　of　inner　defects　of　nugget　is　evaluated　based　on　the　C-scan　image　and　the　time　domain　analysis　of　A-scan　signal.　The　method　proposed　in　the　research　is　not　only　a　comprehensive　and　visualized　method　for　spot　welding　evaluation,　but　also　a　kind　of　important　auxiliary　method　for　spot　weld　research　since　the　inner　structure　of　the　spot　weld　can　be　investigated　without　devastating　it.