Abstract: An ultra performance liquid chromatography-quadrupole-exactive orbitrap mass spectrometry(UPLC-Q-Exactive Orbitrap)was developed for the determination of eighteen kinds of free amino acids in fruits.The crushed samples were extracted by microwave ultrasonic instrument,then centrifugation and filtration,finally,separated on a SHISEIDO CAPCELL PAK BB-H C₁₈(2.1 mm×150 mm,3 μm)column using a binary solvent system composed of 0.2% formic acid aqueous solution and methanol solution by gradient elution. Under this conditions,the analytes were rapidly screened and precisely detected with the precision precursor mass,retention time and two-stage ion mass spectra.The linear range of glycine and alanine was 1~50 nmol/mL,and the linear range of other 16 amino acids was 0.5~50 nmol/mL.There were good linear relationships for the 18 analytes with correlation coefficients(R²)larger than 0.99.The method showed the limit of detection(LOD)was 0.5~1 pmol/g. The recoveries for the 18 compounds at different spiked levels mainly ranged from 79.1% to 118.2%,with relative standard deviations(RSD)of 0.5%~5.6%.The method was convenient,rapid and accurate,and was quite effective for the determination of the 18 free amino acids in fruits,which was beneficial for the investigation on nutritional ingredient in fruits.