The invention discloses a preparation method of a low-cost and high-sensitivity fluorescent/colorimetric dual-mode sensor for visual miRNA detection. The sensor is successfully used for miRNA detection. A paper chip is prepared by utilizing a wax printing technology, platinum nanoparticles grow in a working area of a fluorescent layer, the quenching effect of graphite-phase carbon nitride nanosheets on palladium nanoclusters and duplex specific nuclease are utilized to achieve nucleic acid circulation signal amplification, and accordingly accurate measurement of small molecule miRNA is achieved. The prepared paper chip is folded, and visual predetermination can be achieved by dropwise adding a color developing solution in a reaction area; then the paper chip is placed in a fluorescent dishto achieve accurate fluorescent miRNA determination. The operation is simple, convenient and fast, time and effort are saved, and a new reliable method is provided for miRNA detection.