A method for preparing nano silica and nano calcium carbonate using rice hull ash and flue gas, the method comprising: 1) adding rice hull ash from a biomass power plant to a sodium hydroxide solution having a concentration of between 10 and 20 wt. %, to yield a first mixed solution; stirring and heating the first mixed solution to a temperature of between 95 and 100°C and allowing the first mixed solution to react for 3 to 4 hrs; then filtering the first mixed solution to yield a first filtrate; wherein the rice hull ash comprises between 80 and 90 wt. % of SiO 2, a BET specific surface area thereof is between 40 and 100 m 2 /g, and a crystal structure of SiO 2 is amorphous; 2) adding the first filtrate of 1) to a reaction still, and diluting the first filtrate using water so that a mass percentage concentration of silica of sodium silicate in a diluted reaction solution to be between 8 and 15%; heating the reaction still to 60 to 80°C, and adding polyethylene glycol as a dispersant of a nonsurfactant to the reaction solution to form a reaction mixture, wherein a dosage of the dispersant is between 0.1 and 5 wt. % of a content of silica of the sodium silicate in the first filtrate of 1); introducing flue gas from the biomass power plant at normal pressure to the reaction solution; stirring and allowing the reaction mixture to react for 2 to 4 hrs; filtering the reaction mixture to yield a first filter cake and a second filtrate; washing the first filter cake until it has a neutral pH, slurrying, and spray drying the first filter cake to yield nano silica; and 3) mixing the second filtrate and a washing solution collected from 2) to yield a second mixed solution; adding the second mixed solution to the reaction still and heating the reaction still to 50 to 70°C; adding a calcium hydroxide solution to the reaction still and stirring to allow to react for 0.5 to 2 hrs; filtering and washing a resulting product to yield a second filter cake and a third filtrate; drying the second filter cake in a flash dryer to yield nano calcium carbonate. 1) adding rice hull ash from a biomass power plant to a sodium hydroxide solution having a concentration of between 10 and 20 wt. %, to yield a first mixed solution; stirring and heating the first mixed solution to a temperature of between 95 and 100°C and allowing the first mixed solution to react for 3 to 4 hrs; then filtering the first mixed solution to yield a first filtrate; wherein the rice hull ash comprises between 80 and 90 wt. % of SiO 2, a BET specific surface area thereof is between 40 and 100 m 2 /g, and a crystal structure of SiO 2 is amorphous; 2) adding the first filtrate of 1) to a reaction still, and diluting the first filtrate using water so that a mass percentage concentration of silica of sodium silicate in a diluted reaction solution to be between 8 and 15%; heating the reaction still to 60 to 80°C, and adding polyethylene glycol as a dispersant of a nonsurfactant to the reaction solution to form a reaction mixture, wherein a dosage of the dispersant is between 0.1 and 5 wt. % of a content of silica of the sodium silicate in the first filtrate of 1); introducing flue gas from the biomass power plant at normal pressure to the reaction solution; stirring and allowing the reaction mixture to react for 2 to 4 hrs; filtering the reaction mixture to yield a first filter cake and a second filtrate; washing the first filter cake until it has a neutral pH, slurrying, and spray drying the first filter cake to yield nano silica; and 3) mixing the second filtrate and a washing solution collected from 2) to yield a second mixed solution; adding the second mixed solution to the reaction still and heating the reaction still to 50 to 70°C; adding a calcium hydroxide solution to the reaction still and stirring to allow to react for 0.5 to 2 hrs; filtering and washing a resulting product to yield a second filter cake and a third filtrate; drying the second filter cake in a flash dryer to yield nano calcium carbonate.