Abstract: To solve the problems of long analysis time (about 12 h) and low detection rate when determining polymeric root retardants in asphalt-based waterproof sheets of resistance to root penetration with the group standard T/CBMF 49-2019&T/CWA 301-2019, the method as mentioned by the article was proposed. The sample of 1 g was mixed with methyl tert-butyl ether of 25 mL, and dissolved by ultrasound for 30 min at room temperature. Ethanol of 25 mL was added to the above solution for extraction by ultrasound for 15 min, the mixed solution was filtered with 0.45 μm hydrophobic PTFE filter, and mass fraction of free MCPP acid (w_free) in the filtrate was determined by HPLC. Another sample of 1 g was taken and dissolved with methyl tert-butyl ether by ultrasound for 30 min at room temperature, and 25 mL of ethanol solution containing 0.1 mol·L^-1 NaOH was added to the above solution for extraction by ultrasound for 15 min. The solution obtained was taken out, saponified and hydrolyzed in water bath at 40 ℃ for 1 h. After filtering with 0.45 μm hydrophobic PTFE filter, mass fraction of total MCPP acid (w_total) in the filtrate was determined by HPLC. In HPLC analysis, the system composed of 0.5% (φ) phosphoric acid solution and acetonitrile was used as the mobile phase, and the content of polymeric root retardant was calculated by (w_total-w_free)/0.6. As found by results, the analysis time of the method could be shortened to about 3 h, and linear range of standard curve of MCPP acid was found in the range of 5-100 mg·L^-1, with detection limit (3S/N) of 0.03‰. The proposed method was applied to the analysis of different types of samples from different manufacturers. The determined values were basically the same as the labeling values, and RSDs (n=6) of the determined values were less than 2.0%, with results of test for the spiked recovery in the range of 95.1%-108%.