The instability and rapid consumption of H2O2 limit the application of UV/H2O2 in water treatment. Recently, calcium peroxide (CaO2) has been demonstrated as an effective source of H2O2. However, the performance and mechanism of UV/CaO2 are still unknown. Herein, UV/CaO2 and UV/H2O2 were compared for degradation of aniline. The removal efficiency of aniline by UV/CaO2 was slightly lower than that by UV/H2O2, which could be attributed to the light scavenger by CaO2 suspended particles. HO‧ was identified to participate in aniline degradation in both UV/CaO2 and UV/H2O2, while O2-· was only involved in UV/CaO2. The efficiency of aniline degradation in UV/CaO2 was affected by the released H2O2 in the system. The release and decomposition rate of H2O2 in UV/CaO2 system were influenced by the CaO2 dosage and reaction pH, but slightly related with water matrix. Excessive CaO2 would scavenge aniline degradation through the released H2O2 to react with HO‧. Acidic condition would enhance the concentration of H2O2 in UV/CaO2 and promote the degradation of aniline. Cl– showed slight and almost no effect on aniline degradation in UV/CaO2 and UV/H2O2 systems, respectively, while HCO3– scavenged aniline degradation in UV/CaO2. NO3– inhibited aniline degradation in both UV/CaO2 and UV/H2O2. Compared to UV/H2O2, UV/CaO2 shows the similar efficiency on organics removal but conquers the limitations in UV/H2O2, which is a promising alternative choice in water treatment. Display omitted •Aniline removal by UV/CaO2 was slightly lower than that by UV/H2O2.•Aniline degradation was affected by the released H2O2 in UV/CaO2.•Acidic pH enhanced H2O2 concentration and aniline degradation.•HO‧ and O2-‧ were involved in the degradation process.