Abstract: By optimizing test conditions including water sample acidity, solid phase extraction column type, aqueous phase of mobile phase, and column temperature, the method mentioned by the title was proposed for simultaneous determination of 47 antibiotics in water environment, including 18 sulfonamides, 16 quinolones, 9 macrolides, and 4 tetracyclines. The 1 000 mL of water sample was taken, and passed through a 0.7 μm glass fiber membrane. The filter membrane was washed, and the washing solution and the filtrate were combined. The mixed solution was acidified to pH 2.0±0.5 with hydrochloric acid, followed by addition of ethylenediaminetetraacetic acid disodium salt (0.5 g) and 30 μL of recovery indicator mixed solution containing ¹³C₆-sulfamethoxazole and difloxacin-d₅ with the same mass concentration of 1 000 μg · L⁻¹. The mixed solution was loaded onto activated HLB solid phase extraction column at flow rate of approximately 5 mL · min⁻¹. After washing with 10 mL of water, blowing by nitrogen for 20 min, and eluting sequentially with 12 mL of methanol and 10 mL of mixed solution of acetone and methanol at volume ratio of 1∶1, the eluates were combined and concentrated to near dryness in vacuum. The residue was reconstituted in 20 μL of 1 000 μg·L⁻¹ atrazine-d₅ internal solution and 1 mL of mixed solution of 1.0% (volume fraction, the same below) formic acid solution and acetonitrile at volume ratio of 8∶2. The mixed solution was passed through a 0.22 μm filter membrane, and the filtrate was analyzed by ultra-high performance liquid chromatography-tandem mass spectrometry. The 47 antibiotics were separated on Shim-pack GIST C₁₈ column using gradient elution with mobile phases consisting of 1.0% formic acid solution and mixed solution of methanol and acetonitrile at volume ratio of 1∶1, ionized by electrospray ion source in positive mode, and detected by multiple reaction monitoring mode, with internal standard method for quantification. It was shown that linear relationships between the mass concentrations of 47 antibiotics and peak area ratios of antibiotics to internal standard were kept in the range of 10.0-200 ng·L⁻¹, with detection limits (3.143s) in the range of 0.100-0.400 ng · L⁻¹. Test for recovery was made by the standard addition method, giving recoveries in the range of 75.0%-115%, with RSDs (n=6) of the determined values below 15%. The proposed method was applied to the analysis of 22 water samples from typical urban river monitoring sites in Hangzhou City, 32 antibiotics were detected with maximum detection amount of 138 ng · L⁻¹, and antibiotics with high detection amounts were predominantly found at monitoring sites in densely populated areas.