The invention discloses a method for measuring content of 11 illegally added medicaments in veterinary drug powder. The method comprises the following steps of (1) pre-treating veterinary drug powder to be measured by adopting an organic solvent ultrasonic extraction method, wherein an organic solvent is methanol-water, and a volume ratio of methanol to water is (0.9-1.1):(0.9-1.1); (2) detecting olaquindox, ribavirin, amantadine, rimantadine, dexamethasone, chloramphenicol, diethylstilbestrol, furaltodone, nitrofurantoin, nitrofural and furazolidone in extract by adopting liquid chromatography-tandem mass spectrometry. According to the method, a sample can be simply pre-treated by adopting methanol / water (50+50) as an extraction reagent for ultrasonic extraction, and can be loaded on a machine for detection after passing through a filter membrane, and a recovery rate is high; the method is lower in detection limit, a detection limit of the olaquindox, ribavirin, amantadine, rimantadine, dexamethasone, chloramphenicol, furaltodone and furazolidone is 50mu g / kg, and a detection limit of the nitrofurantoin, nitrofural and diethylstilbestrol is 100mu g / kg.