The　sealing　of　flexible　packages　plays　an　important　role　in　product　quality.　Ultrasonic　non-destructive　testing　technique　is　introduced　to　detect　flexible　package　seal　quality.　The　channel　defects　with　diameters　between　50　μm　and　150　μm　in　the　seal　area　of　flexible　packages　are　detected　using　backscattered　echo　envelope　integral　imaging　method.　The　images　are　formed　with　an　immersion　spot　focused　22.66　MHz　ultrasound　transducer　scanning　over　a　2.98　mm1.5　mm　rectangular　gird.　Theoretical　analysis　for　the　influence　of　the　transducer　lateral　resolution　on　ultrasonic　testing　result　is　carried　out　while　the　scanning　step　size　is　less　than　lateral　resolution　of　the　transducer;　and　the　relation　between　ultrasonic　testing　result　and　actual　defect　size　is　given　in　different　scope　of　defect　size.　The　results　show　that　the　channel　defects　in　flexible　packages　can　be　effectively　detected　using　ultrasonic　backscattered　echo　envelope　integral　imaging　method,　and　the　size　of　defects　on　the　ultrasonic　image　is　larger　than　its　actual　size,　which　is　correlated　with　the　lateral　resolution　of　the　transducer.　The　experimental　results　are　in　good　agreement　with　the　theoretical　analysis.