A method to directly assay circular RNA (circRNA) is proposed in this work by utilizing the 'microRNA (miRNA) sponge' nature of circRNA and by taking the advantage of duplex-specific nuclease. Moreover, miRNA absorption site-mediated hairpin DNA unfolding and nuclease-assisted target recycling have also been designed in this method to amplify the signal readout, thus sensitive assay of circRNA can be achieved in real samples.