The method for the determination of thiourea dioxide in fillings and rice flour food by ultrasonic extraction and liquid chromatography was established in this work. The detection wave length of thiourea dioxide was 274 nm by means of spectral scanning. The target was separated well by gradient elution with HILIC-Z column and 0.2% (V/V) acetic acid aqueous solution and acetonitrile as the mobile phase. The extraction condition of thiourea dioxide in samples was 0.1% (V/V) acetic acid aqueous solution as extraction solution and 30 min ultrasound in ice water bath. The linear relationship of thiourea dioxide in the concentration range of 0~250 mg/L was good and the correlation coefficient was R2=0.9999. The detection limit and quantitative limit were 0.2 mg/L and 0.5 mg/L, respectively. The average recovery was 95.67%~100.37% for the spiked blank sample at three levels (0.5 mg/kg, 1 mg/kg and 5 mg/kg). The relative standard deviation (RSD) was 0.53%~4.45%. The recovery and RSD could meet the requirements of the methodology. Thiourea dioxide was detected in purple potato filling and mungbean filling and the content was 8.30 mg/kg and 236.36 mg/kg, respectively. The method had the advantages of simple operation, good reproducibility and high accuracy and could be used for the determination of thiourea dioxide in food.