Flexible multi-functional nano/micro-systems with integrated energy units and functional sensing/detecting units on a single chip have gained considerable attention recently due to their optimized maximum functionality within a minimized sized chip and excellent mechanical flexibility and stability. In this work, we present a prototype of a flexible integrated on-chip photodetecting system with a reduced graphene oxide (rGO)-based in-plane microsupercapacitor and a CdS nanowire-based photodetector. For the system, the optimized electrodes in the microsupercapacitor were utilized as the source and drain electrodes of the CdS photodetector simultaneously, configuring a minimized self-powered-like visible light photodetector system without external power source. Driven by the microsupercapacitor (volumetric capacitance=8.01F/cm3 and energy density=6.204Wh/cm3), current on/off ratios of 34.50 and 79.81 were obtained for the CdS-based photodetector depending on the number of the microsupercapacitors. The performance of the designed systems exhibited stable photo-current response consistent with the conventional one driven by the external power source, demonstrating the feasibility of the flexible integrated photodetector systems, which are promising for further large-scale and integrated applications.