In this study, we present CdS nanorods/Ti3C2 QDs Schottky heterojunctions as highly efficient photocatalysts for excellent water splitting and photodegradation, where the Ti3C2 QDs as co-catalyst are firmly anchored on the surfaces of CdS nanorods by Polyethyleneimine (PEI). The enhanced hydrophilicity promotes the contact of the photocatalyst and water molecules owing to the introduction of PEI, accelerating the photocatalytic hydrogen evolution. Especially, the apparent quantum efficiency (AQE) can reach 32.1% and 26.2% at 450 and 500 nm, respectively, much higher than those of reported CdS-based photocatalysts. Additionally, the CdS nanorods/Ti3C2 QDs composite exhibits robust performance on the photodegradation of bisphenol A (BPA). The liquid chromatography-mass spectrometer (LC-MS) analysis demonstrates that BPA is oxidized to five byproducts firstly and then the rings are opened sequentially. Furthermore, femtosecond transient absorption (fs-TA) spectroscopy confirms that the formation of Schottky heterojunction between CdS nanorod and Ti3C2 QD, which promotes the migration and separation of photogenerated carriers, leading to the excellent photocatalytic activity. Our findings provide a rational design of heterogeneous photocatalyst with superior photocatalytic performance.