The invention provides a method for measuring silicon concentration in oilfield tri-component complex flooding produced sewage. The method comprises the following steps: establishing a calibration curve by using a silicon dioxide standard solution, and calculating a regression formula; centrifuging the oilfield tri-component complex flooding produced sewage, and taking an intermediate aqueous phase; performing repeated extraction on the aqueous phase by using petroleum ether until the extracting solution is colorless, taking the raffinate, thereby obtaining to-be-measured sewage; adding the quantitative to-be-measured sewage into a colorimetric tube, adding water to achieve the scale, adding a hydrochloric acid solution, mixing uniformly, standing, filtering by using intermediate speed qualitative filter paper, thereby obtaining the filtered solution; adding the filtered solution into the colorimetric tube, adding an ammonium molybdate solution, uniformly mixing, and standing; using a spectrophotometer, taking the reagent blank as reference, measuring solution absorbance at the wavelength of 640nm by using a 1cm cuvette, and calculating the concentration of silicon dioxide in the sewage according to the absorbance, the calibration curve and the regression formula. According to the method disclosed by the invention, interference of impurities in the sewage can be eliminated, and the silicon concentration in the oilfield tri-component complex flooding produced sewage is accurately measured.