In　road　network　planning,　locating　the　key　sections　is　very　useful　to　solve　the　traffic　bottleneck.　Locating　the　key　sections　is　equal　to　finding　the　maximum　flow.　To　begin　with,　this　paper　analyzed　and　compared　kinds　of　methods　solving　the　network　maximum　flow　problem.　Secondly,　this　paper　pointed　out　a　convenient　method　based　on　the　auxiliary　graph　theory　and　Dijkstra　method.　That　is　to　say,　the　method　could　be　used　to　get　the　minimum　cutset　and　the　maximum　flow　using　the　shortest　path　algorithm,　and　the　VC　+　+　program　was　also　used.　Finally,　based　on　the　road　network　of　Tianjin,　an　example　was　given　for　further　explanation.　Through　comparison,　it　can　be　found　that　it　is　a　convenient　method　to　locate　the　key　sections,　and　can　support　the　transportation　planning　and　management　with　theoretical　basis　and　data.