The invention discloses a novel nanocomposite C60@ polyamidoamine dendrimer (PAMAM)-metal organic framework (MOF) of iron-based MOF and amino-terminated PAMAM functionalized fullerene (C60), and further discloses a preparation method and application of an electrochemical microRNA biosensor. According to the biosensor, nanogold is supported in the material C60@PAMAM-MOF, the nano material and a sulfhydryl-marked signal probe are mixed and stirred, a tracer marker of the biosensor is prepared through Au-S key bonding, a capture probe is further supported on a sensing interface assembled by chitosan-acetylene black and platinum putamen nanoparticles, and the biosensor for detecting miR-3675-3p is constructed through nucleic acid hybridization. The sensor prepared by taking the C60@PAMAM-MOF as the nanoprobe has the higher signal amplification effect, and further has the advantages of wide linearity range, high specificity, short analysis time and the like, and a new method can be providedfor diagnosis of idiopathic pulmonary fibrosis.