The　development　of　a　convenient　and　sensitive　biosensing　system　to　detect　specific　DNA　sequences　is　an　important　issue　in　the　field　of　genetic　disease　therapy.　As　a　classic　DNA　detection　technique,　molecular　beacon　(MB)　is　often　used　in　the　biosensing　system.　However,　it　has　intrinsic　drawbacks,　including　high　assay　cost,　complicated　chemical　modification,　and　operational　complexity.　In　this　study,　we　developed　a　simple　and　cost-effective　label-free　multifunctional　MB　(LMMB)　by　integrating　elements　of　polymerization　primer,　template,　target　recognition,　and　G-quadruplex　into　one　entity　to　detect　target　DNA.　The　core　technique　was　accomplished　by　introducing　a　G-hairpin　that　features　fragments　of　both　G-quadruplex　and　target　DNA　recognition　in　the　G-hairpin　stem.　Hybridization　between　LMMB　and　target　DNA　triggered　conformational　change　between　the　G-hairpin　and　the　common　C-hairpin,　resulting　in　significant　SYBR-green　signal　amplification.　The　hybridization　continues　to　the　isothermal　circular　strand-displacement　polymerization　and　accumulation　of　the　double-stranded　fragments,　causing　the　uninterrupted　extension　of　the　LMMB　without　a　need　of　chemical　modification　and　other　assistant　DNA　sequences.　The　novel　and　programmable　LMMB　could　detect　target　DNA　with　sensitivity　at　250　pmol/l　with　a　linear　range　from　2　to　100　nmol/l　and　the　relative　standard　deviation　of　7.98%.　The　LMMB　could　sense　a　single　base　mutation　from　the　normal　DNA,　and　polymerase　chain　reaction　(PCR)　amplicons　of　the　mutant-type　cell　line　from　the　wild-type　one.　The　total　time　required　for　preparation　and　assaying　was　only　25　minutes.　Apparently,　the　LMMB　shows　great　potential　for　detecting　DNA　and　its　mutations　in　biosamples,　and　therefore　it　opens　up　a　new　prospect　for　genetic　disease　therapy.