MicroRNAs play a crucial role in regulating plant growth, such as involving in the pathways of phytohormons signaling, which function in broad range of important aspects in many stages of plant development and evolution. To figure out the components part of microRNA in phytohormone signaling network, a sensitive photoelectrochemical biosensor was developed to detect miRNA-319a specifically using CuO-CuWO4 as photoactive material and in situ generation electron donor technique. Taking the advantage of rolling circle amplification, nicking endonuclease triggered exponential amplification of target molecule, specific interaction between phosphate group and phos-tag and between biotin and avidin, the developed strategy can greatly amplify the detection signal only using trace amount of target miRNA-319a. The wide linear range was obtained from 1 fM to 0.1nM and the detection limit was estimated to be 0.47 fM (S/N=3). The developed method also showed good detection specificity. The effect of five phytohormones on the expression level of miRNA-319a in rice leaves was also investigated. This will be a basal principle of investigating the signaling network of phytohormones.