A method of determination of hydrazine， monomethylhydrazine （MMH）， and unsymmetrical dimethylhydrazine （UDMH） in water by hydrophilic interaction chromatography （HILIC） coupled with mass spectrometry （MS） was developed. Sample preparation， composition of mobile phase and parameters of MS detection were investigated for optimization for HILIC-MS analysis of hydrazine compounds. 80% isopropanol-0.1% formic acid was used as sample solvent， and injection volume was 10 μL. Composition of mobile phase was 70% acetonitrile-10 mmol·L^-1 ammonium formate， pH=3.5. Hydrophilic interaction chromatographic column was utilized for separation. Protonated non-covalent adduct of hydrazine and acetonitrile， protonated MMH and protonated UDMH were selected as detection ions， and post-source collision energy were 50， 100， 100 eV， respectively. Good linearity between MS response intensity and analyte concentration for quantitative analysis was obtained in certain range of analyte concentration. The limits of detection for hydrazine， MMH and UDMH were 0.04， 0.005， 0.025 mg·L^-1， respectively. Recovery of spiked water sample was determined as 92%-115%.