The　current　cancer　detection　methods　are　heavily　dependent　on　the　component　analysis　of　corresponding　cancer　antigens.　There　is　a　lack　of　effective　and　simple　clinical　methods　of　ovarian　cancer　screening,　which　hinders　the　early　identification　for　ovarian　cancer　and　its　treatment.　To　develop　a　simple　and　rapid　method　for　quantitative　analysis　of　ovarian　cancer,　we　developed　a　DNA　strand　displacement-based　method　and　finished　the　rapid　detection　of　miR-21　in　ovarian　cancer　cells　within　5　min　by　a　one-step　isothermal　reaction.　The　fluorescence　intensity　trajectory　had　a　good　linear　relationship　with　miR-21　concentrations　in　the　range　of　100　fM-100　nM,　with　a　lower　limit　of　6.05　pM.　This　detection　method　is　simple,　faster,　and　accurate.　Besides,　it　can　be　applied　to　detect　the　miRNA　biomarkers　of　other　cancers　by　changing　the　preset　sequences　of　toehold.