An ultrahigh performance liquid chromatography coupled with quadrupole orbitrap mass spectrometry（UHPLC/ESI－Q－Orbitrap） was established for the detection of selenomethionine in beans，by collecting the chromatographic information，mass charge ratio of molecular ion and mass charge ratio of fragmentation fragments of selenomethionine（SeMet） and analyzing the fragmentation pathway．The samples were firstly dissolved with Tris－HCl buffer solution，then blended well with a vortex mixer，followed by ultrasonic extraction and enzymatic hydrolysis under constant temperature bath with trypsin and protease K，and finally centrifuged．The supernatant was filtered through a 0.22 μm microporous membrane，and then determined using the UHPLC/ESI－Q－Orbitrap system．The extract was separated on an Hypersil GOLD HILIC column（50 mm × 2.1 mm，1.9 μm） by gradient elution，using 0.2%（volume fraction） formic acid－6 mmol/L ammonium formate aqueous solution and 0.2% formic acid－6 mmol/L ammonium formate acetonitrile solution as the mobile phases．The SeMet was determined in positive electrospray ionization mode（ESI） under Full MS/dd－MS,2, acquisition mode，and quantified by matrix-matched standard calibration method due to the existence of matrix effect．The matrix effect for SeMet was 15.75%，evaluated by the ratio of solvent standard curve and matrix-matched standard curve．Under the optimal conditions，there was a good linear relationship for SeMet in the concentration range of 0.05－0.5 mg/L with a correlation coefficient（,r,2,） of 0.997 6，while the limit of detection（LOD） and the limit of quantification（LOQ） were 0.015 mg/kg and 0.05 mg/kg，respectively．At three spiked levels of 0.1，0.2 and 0.4 mg/kg，the average recoveries for SeMet in mung bean ranged from 77.6%－83.2%，with the intra-day relative standard deviations（RSD,r,） and the inter-day relative standard deviations（RSD,R,） of 2.8%－4.8% and 4.1%－6.5%，respectively．This method was applied to the detection on actual samples collected in laboratory．The results showed that the contents of selenomethionine in selenium-enriched black bean，selenium-enriched red bean and selenium-enriched mung bean were 0.252，0.163 and 0.184 mg/kg，respectively．With the advantages of simple pretreatment，accurate result and good repeatability，this method is suitable for the detection of SeMet in beans.