Pyrethroid accumulation in body will cause harm to human nerves and skin， and even mutation， resulting in birth defects and cancer. λ-Cyhalothrin is a typical pyrethroid insecticide， and the residue in food has attracted widespread public attention. An analytical method was established for the determination of λ-cyhalothrin residues in tea by high performance liquid chromatography. The chromatographic conditions was chosen Inertsil ODS-C18（150 mm × 4.6 mm， 4.6 μm）， chromatographic column using water （1% formic acid） -methanol （15 ∶ 85， V/V） as mobile phases， detection wavelength was 210 nm and velocity was 0.5 mL/min. The optimum ultrasonic conditions are as follows： the ratio of material to liquid is 1 ∶ 10 （g/mL）， the ultrasonic power is 80 kHz， the ultrasonic time is 40 min， and the ultrasonic temperature is 20 ℃. The results showed that the linear range of λ-cyhalothrin was 1~100 μg/L and the correlation coefficient was 0.9998. The average recoveries ranged from 76% to 103% with relative standard deviation less than 3.853%， the LOD and LOQ were 0.2 μg/L and 1 μg/L， respectively.