High sensitivity of biosensor is one of the most vital factor to realize the accurate detection of biomarkers. To achieve this purpose, enhancing initial signal and amplifying the value of signal change are two main approaches. In this work, the Mn doped CdS sensitized Ti O2/ITO electrode was employed as ideal photoactive matrix, which can provide a stable and enhanced basal signal. To achieve the amplification of signal change value, thrombin aptamer modified AuNPs composites(AuNPs-TBA) was used as a quencher to construct a PEC biosensors, which was prepared via a convenient self-assembly way. On account of the energy transfer between AuNPs and CdS, besides, the steric hindrance effect of that conjugates obstructed the electron transfer from the electron donors to the photoelectrode surface, leading to a further decrease of photocurrent. The as-prepared PEC biosensor for thrombin exhibited high sensitivity and excellent stability with a low detection limit of 30 fM. Additionally, the strategy provided an efficient and simple approach for signal amplification and held great promise for other PEC biosensor development.