In this paper, by a radio frequency magnetron sputtering equipment, the ZnO/Pt nanoparticles/ZnO thin film structure is fabricated on a SiO2 substrate via three-step. And the metal-semiconductor-metal (MSM) structured ultraviolet (UV) photodetectors are built up. It is studied that the Pt nanoparticles in different depths of the layer of ZnO thin film affect the photoresponse performances of the MSM ultraviolet photodetector. The results show that the responsivity of the detector increases as Pt nanoparticles in ZnO thin film layers augment with the depth increasing. The responsivity of device is measured under 60 V bias, its photoresponse peak is at 365 nm, and the peak photoresponse is 1.4 A·W-1, which is enhanced by 7 times that of the photodetector without Pt NPs. Considering the performance analyses of ZnO films and the photodetectors, it is clear that the excellent performances of the detector with Pt NPs in the film can result from the scattering of Pt NPs.