In order to avoid the time-consuming，expensive equipment and complicated steps of traditional lithography and to solve the neck-pinching technical problems in the field of microelectronics fabrication，liquid-surface self-assembled polystyrene（PS）nanosphere is utilized to prepare nanostructured arrays in this paper. Low-cost，large-area，size-controllable nanostructured arrays on n-type silicon substrates are successfully prepared and successfully employed to photodetector. It is shown that the introduction of nanostructures can effectively improve the anti-reflective property of silicon surface，and the reflectivity is reduced by up to about 96% compared with that of planar silicon. The light/dark current ratio of the nanostructured device approximately reached one order of magnitude. At +5 V bias，the responsivity of the nanostructured photodetector is improved by 10.1-fold and 3.7-fold compared with that of the planar one at the wavelengths of 365 nm and 405 nm，respectively. At +5 V bias，the external quantum efficiency（EQE）of the nanostructured photodetector is 10.1 times higher than that of the planar one at 365 nm and 3.7 times higher at 405 nm. This provides a low-cost，efficient，reliable and simple way to prepare high-performance nanostructured optoelectronic devices.