The invention discloses a detection method for measuring the silicon content in a water body and a silicon dioxide content analysis device. The device comprises a chemical reaction mechanism, a chromometer and a data processing mechanism, wherein the chemical reaction mechanism comprises a plurality of medicine kits, a reaction tank and a sampling water storage tank, the medicine kits are used for storing different medicaments and at least comprise a first medicine kit and a second medicine kit, the first medicine kit is used for storing an ammonium molybdate agent and an oxalic acid agent, the second medicine kit is used for storing 1-2-4 acid, all the medicine kits are communicated with the reaction tank by respectively connected liquid medicine conveying tubes, and medicine feeding pumps are arranged on the liquid medicine conveying tubes respectively; a liquid level meter is arranged in the sampling water storage tank which is communicated with a water sample mechanism containing silicon dioxide by a plurality of sampling input pipelines, and first solenoid valves and regulating valves are arranged on the sampling input pipelines; the sampling water storage tank is communicated with the reaction tank by a sample liquid conveying tube, and a second solenoid valve is arranged on the sample liquid conveying tube; the chromometer is arranged on the side surface of the reaction tank and measures the color of a silicon molybdenum blue solution; the data processing mechanism controls all the parts of the device.