A crosslinked β-cyclodextrin polymer (β-CD-MDI), synthesized by the modification of β-cyclodextrin (β-CD) with crosslinking reagent diphenyl methane diisocyanate (MDI), was prepared and used as an adsorbent in the treatment of phenol wastewater ultrasonic aided. An infrared spectroscopy test was conducted to characterize β-CD-MDI. The adsorption capacity of phenol in wastewater was determined by assessing the corresponding parameters, such as the amount of adsorbent β-CD-MDI, the initial concentration of phenol, the influence of pH and ultrasonic intensity. The adsorption efficiency of β-CD-MDI is up to 87.3% with an amount of crosslinked polymer of 40 g/L, an initial phenol concentration of 100 mg/L and a wastewater pH of 6. The application of ultrasound can facilitate the purification of wastewater and reduce the adsorption time remarkably.