The ability to rapidly detect apoptotic cells and accurately evaluate therapeutic effects is significant in cancer research. To address this target, a biocompatible, ultrasensitive photoelectrochemical (PEC) cytosensing platform was developed based on electrochemically reduced graphene (EG)/ZnIn2S4 co-sensitized TiO2 coupled with specific recognition between apoptotic cells and phosphatidylserine (PS)-binding peptide (PSBP). In this strategy, HL-60 cells were selected as a model, and C005, nilotinib and imatinib were selected as apoptosis inducers to show cytosensing performance. In particular, a TiO2 photoactive substrate was designed as hollow spheres to enhance the PEC performance. Graphene was electrodeposited on the hollow TiO2-modified electrode to accelerate electron transfer and increase conductivity, followed by in situ growth of ZnIn2S4 nanocrystals as photosensitizers via successive ionic layer adsorption and reaction (SILAR) method, forming a TiO2/EG/ZnIn2S4 co-sensitized structure that was used as a PEC matrix to immobilize PSBP for the recognition of early apoptotic cells. The detection of apoptotic cells was based on steric hindrance originating from apoptotic cell capture to induce an obvious decrease in the photocurrent signal. The ultrahigh sensitivity of the cytosensor resulted from enhanced PEC performance, bioactivity, and high binding affinity between PSBP and the apoptotic cells. Compared with other assays, incorporate toxic elements were avoided, such as Cd, Ru, and Te, which ensured normal cell growth and are appropriate for cell analysis. The designed PEC cytosensor showed a low detection limit of apoptotic cells (as low as three cells), a wide linear range from 1×103-5×107 cells/mL and an accurate evaluation of therapeutic effects. It also exhibited good specificity, reproducibility, and stability.