Based on the synergistic effect of pulsed discharge plasma and titanium dioxide (TiO2) photocatalysis, a coupling system of pulsed discharge plasma/TiO2 was set up in the present paper, by using the ultraviolet radiation produced during the pulsed discharge process. TiO2 film immobilized on the glass beads was used as the photocatalyst in the synergistic system. In the research, the synergistic mechanism of pulsed discharge plasma and TiO2 photocatalysis was reviewed by the spectral diagnosis of oxygen radical (·O radical) produced in different reaction systems. The obtained results showed that the characteristic emission spectrum of ·O radical could be observed at 777 nm and the corresponding transitions was 3p5P→3s5S. When air was used as bubbling gas, the relative emission intensity of ·O radical recorded in the synergistic system was stronger than that in the plasma alone system, and the same result was also obtained when oxygen (O2) was used as bubbling gas. This result revealed that the photocatalytic activity of the immobilized TiO2 in the synergistic system could be induced by the ultraviolet radiation formed during the pulsed discharge process. In the systems of pulsed discharge plasma alone and pulsed discharge plasma combined with TiO2 photocatalysis, the relative emission intensity of ·O radical in distilled water was stronger than that in phenol solutions. The results showed that ·O radical was one of responsible radicals for phenol degradation in the pulsed discharge plasma alone system as well as the synergistic system.