Nano-polysilicon dispersible in water was synthesized and resultant nano-polysilicon was used for decompression and augmented injection of the water-injection wells in low-permeability reservoir with water as a replacement carrier of organic dispersant.Based on the analysis of pore-throat characteristics in Baolang reservoir,it was suggested that the size of nano-polysilicon should be 10—20 nm so as to well match with the size of pore-throat.Besides,the nano-polysilicon emulsion was transparent.Through the study of dispersion capacity and stability of the emulsion,the formula of nano-polysilicon water-based decompression and augmented injection fluid was: 1.75 ‰ nano-polysilicon and 2‰ assistant dispersant.After being treated with nano-polysilicon water-based emulsion,it was feasible to convert the hydrophilic core surface into a great hydrophobic with contact angle increasing from 23.7° to 131.8°.Core flow tests showed that the water permeability increased by 40% in average after being treated with this fluid.For sewage injection well and water injection well changed from oil well,it was supposed that an excellent decompression and augmented injection effectiveness could be achieved when pre-acidizing was done before nano-liquid augmented injection.Field test in Baolang oilfield indicated that the title augmented injection agent was able to increase the augmented injection effectiveness by a rate of 80% and could retain effectiveness in more than one year.