Converting solar energy into chemical energy by artificial photosynthesis is promising in addressing the issues of the greenhouse effect and fossil fuel crisis.Herein,a novel photocatalyst,i.e.CdS/TiO2 hollow microspheres (HS),were dedicatedly designed to boost overall photocatalytic efficiency.TiO2 nanoparti-cles were in-situ decorated on the inside and outside the shell ofCdS HS,ensuring close contact between TiO2 and CdS.The CdS/TiO2 HS with abundant mesopores inside of the shell boost the light absorp-tion via multiscattering effect as well as accessible to reactions in all directions.The heterojunction was scrutinized and the charge transfer across it was revealed by in-situ irradiated X-ray photoelectron spectroscopy (ISI-XPS).Ultimately,the charge transfer in this composite was determined to follow step-scheme mechanism,which not only facilitates the separation of charge carriers but also preserves strong redox ability.Benefited from the intimate linkage between CdS and TiO2 and the favorable step-scheme heterojunction,enhanced photocatalytic CO2 reduction activity was accomplished.The CH4 yield rate of CdS/TiO2 reaches 27.85 μmol g-1 h-1,which is 145.6 and 3.8 times higher than those of pristine CdS and TiO2,respectively.This work presents a novel insight into constructing step-scheme photocatalytic system with desirable performance.