The rapid recombination of carriers on plasmon metal nanoparticles significantly decreases the efficiency of traditional photocatalysts. The separation of hot electrons and holes can be achieved by recombining metal and semiconductors, improving the efficiency of photocatalysis. This paper combined Ag and TiO2 nanoparticles to improve the photocatalytic activity. The enhanced mechanism of the catalytic activity was explored. The effect of energy band bending in the space charge region between TiO2-Ag nanocomposites and the built-in electric field was studied, which provided a theoretical and experimental basis for designing high-performance SPR photocatalysts. Furthermore, the photocatalysis coupling reaction of PATP and PNTP was employed to study the catalytic performance of TiO2-Ag nanocomposites. The results reveal that the introduction of TiO2 improves the SPR catalytic activity of Ag. The main reason is that introducing TiO2 can improve the separation efficiency of electrons and holes between TiO2 and Ag.