When cavities collapse, the radicals of ·OH and ·H are generated. The hydroxyl radical with strong oxidizing property can react with refractory organic compound molecule, and it has a direct relevant to cavitation effect. With choking cavitator as the cavitation generator and methylene blue (MB) as free radical scavenger, applied visible spectrophotometer to detect MB mass concentration before and after the reaction, obtained indirectly hydroxyl radical production, and investigated the influences of the initial concentration of MB, equivalent diameter of back-pressure holes and reaction time on hydroxyl radical production. The experimental results showed that the highest hydroxyl radical was acquired when the equivalent diameter of back-pressure holes was 5.4 mm and the initial concentration of MB was 12 mg/L.