The combination of inorganic perovskite and graphene oxide has been demonstrated to be an efficient strategy for obtaining excellent optical and electrical properties. In this work, high-quality CsPbBr3 nanocrystals are loaded on graphene oxide (GO) to form GO-CsPbBr3 nanocomposites by post-mixing of the two materials. The photoluminescence spectra indicated that GO could dramatically quench the luminescence of the pristine-CsPbBr3 nanocrystals in the GO-CsPbBr3 nanocomposites, which is probably induced by the fast separation and transfer of the photogenerated hole–electron pair. The fast separation and transfer of the photogenerated hole–electron pair between GO and CsPbBr3 nanocrystals have been confirmed by an ultrafast transient absorption study, and a lifetime τ = 18.6 ± 4.1 ps of electron transfer from CsPbBr3 nanocrystals to GO could be obtained. In addition, the GO could significantly boost the photocurrent intensity; the photocurrent of GO-CsPbBr3 nanocomposites is about 2.5 times that of the pristine-CsPbBr3 nanocrystals. Photoelectrochemical switching on and off can be achieved by using intermittent visible light exposure. These results reveal that GO may act as an electron collector to extract electrons from CsPbBr3 nanocrystals, suggesting a new potential application of GO-CsPbBr3 nanocomposites for photocatalysis.