Aiming　at　the　effect　of　pixel　defects　on　the　display　of　electrowetting　electronic　paper,　an　automatic　threshold　detection　method　based　on　Otsu　is　proposed　to　detect　defects.　Otsu　is　a　commonly　used　automatic　threshold　method　that　gives　satisfactory　results　when　the　image　histogram　is　bimodal.　However,　the　electrowetting　defect　image　histogram　is　usually　a　single　peak,　and　Otsu　method　fails.　Electrowetting　differs　from　the　background　contrast　due　to　the　filling　inks　of　different　colors,　making　segmentation　more　difficult.　In　this　paper,　the　weighting　coefficient　is　introduced　before　the　target　variance,　and　the　weight　decreases　as　the　cumulative　probability　of　defects　increases.　The　weight　keeps　a　large　value　before　the　threshold　crosses　the　peak,　and　the　weight　decreases　after　the　peak,　ensuring　that　the　threshold　is　always　to　the　left　of　the　peak　in　the　case　of　a　single　peak.　The　experimental　results　show　that　the　proposed　method　can　effectively　segment　the　electrowetting　defect　region,　especially　in　the　electrowetting　defect　image　with　lower　contrast　ratio.　The　method　is　closer　to　0　compared　to　the　ME　value　of　Otsu,　VE,　WOV　and　entropy　weighting　methods.　The　proposed　method　has　a　better　segmentation　effect.　©　2020,　Editorial　Office　of　Opto-Electronic　Engineering.　All　right　reserved.