In this article, low-pressure control methods for a combined arc submerged nanoparticle synthesis system (ASNSS) was proposed and developed for TiO2 nanoparticle fabrication. The photocatalytic reaction is carried out in a photochemical reactor. The UV light is obtained from UV-lamps with wavelength of (253.7±0.8) nm. The UV-Vis spectrometry is used to monitor the absorbance spectra of methylene blue as a function of illumination time. Experimental results show that the rate constant of photocatalytic reaction of TiO2 nanoparticles for methylene blue is 0.0365 min-1.The surface adsorption plays an important role in the decomposition of methylene blue. Experimental results indicate that the TiO2 nanoparticle fluid possesses excellent photocatalytic activity in photodegradation of methylene blue.