MicroRNA (miRNA) is promising candidate for non-invasive diagnostic biomarker. Conventional CRISPR/Cas12a-based miRNA detection systems are constrained by reliance on reverse transcription, nucleic acid pre-amplification and costly fluorescently labeled reporters which introduce chemical modification complexity and background noise. To address these limitations, we herein developed a multifunctional switch that integrated target recognition, CRISPR/Cas12a system activation, intrinsic fluorescence signaling, and autonomous signal amplification within a single molecular architecture. As a proof of concept, this switch enabled a label-free CRISPR/Cas12a biosensing for miR-21 detection with a detection limit of 4.8 nM and robust performance in accuracy, precision, and selectivity. This proposed label-free CRISPR/Cas12a platform could be applied for real sample and is a promising candidate for point-of-care miRNA detection.