As for the problem that the detection method of residual monomer of water-soluble polymer was too targeted，a method for simultaneous determination of maleic acid，fumaric acid and itaconic acid in water-soluble polymer used in drilling fluid by HPLC was established. The experimental conditions were obtained as follows：the water-soluble polymer was extracted with acetonitrile for 30 min，and the mobile phase contained 0.1% phosphoric acid and acetonitrile at volume ratio 85∶15. Agilent Zorbax Eclipse XDB C18 column（250 × 4.6 mm，5 μm）was used，and the flow rate of column was 0.8 mL/min，the column temperature was 45 ℃，and the detection wavelength was 210 nm. Under the above experimental conditions，the detection results had good separation characteristics（the separation degree was greater than 3），good linear relationship（the R² value was greater than 0.999）and good stability（the RSD was less than 1%）. The minimum detection limit of maleic acid，fumaric acid and itaconic acid were 0.32，0.34 and 0.63 mg/kg. the quantitation of maleic acid，fumaric acid and itaconic acid were 1.21，1.26 and 2.02 mg/kg. The recoveries of the three residual monomers were 98%—101%. The mass fractions of the three residual monomers in a sample of the viscosifier were 2.261%，0.284% and 2.775%. The time of chromatographic detection was less than 10 min，and it could meet the quality control of the water-soluble polymer. The method could accurately control the synthesis process of water-soluble polymers and achieve accurate quality control.