In the present work, a novel signal-on photoelectrochemical (PEC) sensing scaffold was developed for sensitive detection of target DNA by cycling amplification strategy, in which the CdS quantum dots (QDs) labeled DNA was served as a highly efficient photoactive species. The Au nanoparticles (NPs) with excellent electroconductibility were introduced to the sensing platform to improve the photocurrent, and the endonuclease-aided cycling amplification strategy was further applied to amplify the detection signal. Under the optimized conditions, this "signal-on" PEC bioassay showed a linear relationship between photocurrent and the target concentration in the range of 0.001-100 nM. The developed PEC bioassay with high sensitivity and good specificity has a great potential for detecting biomolecules with trace amounts in bioanalysis and clinical biomedicine.