A kinetic equation for ultrasonic-assisted extraction process was presented based on Fick’s first law of diffusion.The kinetics of ultrasonic-assisted extraction process agreed with the first-order rate equation.Experiments for extracting chlorogenic acid from the leaves of Eucommia ulmoides were studied under different conditions to evaluate the kinetic equation.Experiment data could partly match the kinetic equation.It provided a theoretical reference for the ultrasonic-assisted extraction of Chinese traditional medicine.