Surface plasmon polariton(SPP) is electro-magnetic wave coupled to free electron oscillations near the surface of metal, and has been used to improve the photoelectric properties in many optoelectronic devices. In the present study, the Au nanoparticles(NPs)/β-Ga_2O_3 composite thin film was fabricated through depositing Au ultra-thin film on the β-Ga_2O_3 thin film followed by post-thermal treatment. Compared to bare β-Ga_2O_3 thin film, a significant absorption around 510 nm, which is attributed to SPP of Au NPs, was observed in the UV–vis spectrum of Au NPs/β-Ga_2O_3 composite thin film. The results showed that the photoresponse of Au NPs/Ga_2O_3 photodetector illuminated under 254 nm +532 nm light was much higher than that illuminated under 254 nm light, indicating an enhancement of photoelectric property for the solar-blind photodetector based on β-Ga_2O_3 thin film. Surface plasmon polariton (SPP) is electro-magnetic wave coupled to free electron oscillations near the surface of metal, and has been used to improve the optical properties in many optoelectronic devices. In the present study, the Au nanoparticles (NPs) / β- Compared to thin β-Ga 2 O 3 thin films, a significant absorption around 510 nm, which is attributed to SPP of Au NPs, was observed in the UV-vis spectrum of Au NPs / β-Ga_2O_3 composite thin film. The results showed that the photoresponse of Au NPs / Ga_2O_3 photodetector illuminated under 254 nm +532 nm light was much higher than that of light below 254 nm light, indicating an enhancement of photoelectric property for the solar-blind photodetector based on β-Ga 2 O 3 thin film.