Abstract: An analytical method for the determination of theanine in tea-extraction by HPLC with compensate after column and charged aerosol detector (CAD) was developed.The results showed that the calibration formula was Y=0.1412X-0.0614, the correlation coefficient was above 0.9998, and the calibration curve was linear in the range of 1.50 ~ 50.0μg/mL, and the detection limit of the method (calculate with S/N=3) was 0.50μg/mL, and limit of quantitation was 1.50μg/mL (calculate with S/N=10) .Then a sample was analyzed with this method, and the recoveries of blank sample spiked were 97.62% ~ 112.13%, and the difference of retention time was less than 0.2min and the relative standard deviation of peak area was 0.62% (n=5) .The sensitive and accurate method was successfully applied to the analysis of theanine in tea-extraction.