Introduction The quantitative analysis of trace resveratrol and polydatin in plant tissues is suitable for elucidation of the compounds' mechanisms of action. Objectives The main objective of this work was to develop a feasible and effective sample pretreatment method to measure the concentrations of resveratrol and polydatin in complex samples. Methodology A polymer sorbent, poly(2‐mercaptobenzimidazole), was electrochemically prepared and utilized for selective extraction, while resveratrol and polydatin were used as target analytes. The sorbent was characterized by cyclic voltammetry, scanning electron microscopy and Fourier transform infrared spectroscopy. After extraction and elution, the analytes were analyzed by a Thermo U3000 HPLC system. Several affecting parameters, including the volume of elution solution, sample pH value, sample flow rate and sample volume, were evaluated and optimized. Results The proposed method showed good linearity with low limits of detection (from 0.5 to 0.8 ng·mL−1) and ideal accuracy with spiked recoveries from 81.30% to 99.16%. A good enrichment factor (more than 200‐fold) together with good sensitivity was obtained with this method. Analysis of resveratrol and polydatin in Polygonum cuspidatum samples by this method is efficient. Conclusion The method developed in this work exhibits several significant merits, including easy operation and high extraction efficiency, indicating that electrochemically prepared polymer sorbent is useful for sample pretreatment and analysis of traditional Chinese medicine samples.