In　order　to　solve　the　problem　that　the　existing　automatic　image　cropping　algorithm　mistakenly　cuts　off　the　whole　person　or　part　of　the　body　parts　of　the　main　figure,　which　leads　to　the　missing　of　the　key　information　of　the　image　and　the　poor　composition　of　the　image,　this　paper　proposes　a　real-time　automatic　image　cropping　method　based　on　portrait　detection.　This　method　divides　image　cropping　into　two　stages:　portrait　detection　and　intelligent　composition.　It　aims　to　take　the　extracted　portrait　coordinate　information　as　the　input　of　the　intelligent　cropping　algorithm,　and　then　combines　the　composition　rule　based　on　aesthetics　to　automatically　compose　the　picture,　so　as　to　ensure　the　integrity　of　the　portrait　information　in　the　cropping　result　and　improve　the　composition　beauty　of　the　picture.　The　experimental　results　show　that　the　lightweight　detection　network　modified　on　the　basis　of　Center-Net　in　this　paper　reduces　the　computation　amount　by　86%　and　improves　the　accuracy　by　3.　34%,　which　is　convenient　to　apply　the　cropping　algorithm　to　mobile　devices.　The　FPS　of　the　whole　cropping　algorithm　reaches　77,　and　the　cropped　portrait　information　is　complete,　and　the　overall　composition　of　the　picture　is　improved.