In this work, a new fluorescence biosensor platform based on distance-dependent photoinduced-electron transfer (PET) coupled with target cross-chain displacement cyclic amplification strategy was developed to detect MicroRNA. The DNA cross structure was cleverly designed to protect restriction site, then multiple amplification reactions of target cycle and chain replacement based on DNA cross-configuration were carried out in the presence of primer, polymerase and cutting enzyme, thus a large number of single-stranded (ss) DNA products (S1 and S2) can be exported by inputting a small amount of target miRNA. The fluorescent AgNCs/DNA probe was synthesized based on high affinity of Ag to cytosine (C) rich in ssDNA acting as electron donor, and guanine (G) rich ssDNA can form G-quadruplex complex acting as electron receptor to induce PET process. S1 and S2 hybridized with flexible single-stranded DNA COM 1 and Com 2, forming rigid double-stranded DNA to inhibit fluorescence quenching PET process, so the corresponding fluorescence was recovered. Thus the miRNA-induced amplified products can specifically result in fluorescence changes by PET, and the changes increase with increasing miRNA concentration. Therefore, the proposed fluorescent biosensor can be applied to quantitative determination of miRNA-182-5p, which has great potential in early clinical diagnosis of miRNAs related diseases.