Catalytic oxidation and AOPs normally require catalysts or chemical oxidants during VOCs degradation, making these processes costly and complex. We herein developed a facile system, VUV photolysis in pure water (VUV/H2O), for efficient VOCs degradation without auxiliary substances. The performance and mechanism of this system was intensively studied through controlling reaction conditions, detecting intermediates and analyzing reaction process during toluene degradation. Compared with direct VUV photolysis of gaseous toluene (VUV/Gas), the VUV/H2O system exhibited higher removal efficiency (83%) and mineralization rate (80%) of gaseous toluene bubbled into the system. In addition, no O-3 and gaseous byproducts were detected in the outlet gas stream. The excellent performance of VUV/H2O was attributed to the generation of more OH from the VUV photolysis of water and the continuous degradation of accumulated intermediates dissolved in water. The high CO2 yield under an air atmosphere demonstrated that the dissolved oxygen in the water was essential for toluene mineralization since it was involved in the ring-fragmentation of toluene. According to various radicals and organic intermediates detected, possible pathway of toluene degradation in the VUV/H2O system was also proposed, which include OH addition, hydrogen abstraction and isomerization. The water after reaction can be effectively purified by sustaining VUV irradiation. This study presents a facile VUV/H2O system without auxiliary substances for efficient VOCs degradation and provides an insight into its degradation mechanism.