A　stable　isotope　dilution　technique　based　on　purge-and-trap　coupled　to　gas　chromatography　with　mass　spectrometric　detection　was　developed　and　optimized　for　the　trace　determination　of　the　typical　odorous　compounds,　geosmin　(GSM)　and　2-methylisoborneol　(MIB).　The　selection　of　quantitation　ions　and　the　factors　of　temperature　program,　the　sample　purge　temperature,　salt　content　on　the　extraction　of　odorous　compounds　were　studied.　Under　the　experimental　conditions,　the　optimal　operating　conditions　were　the　addition　of　20%　(　m/V)　NaCl,　purging　at　60　degrees　C　on　the　temperature　program　of　5　degrees　C/min.　D5-Geosmin　and　d3-MIB　as　the　isotopes　internal　standards　were　added　to　improve　the　stability　of　recovery.　Using　this　method,　both　the　calibration　curves　of　MIB　and　GSM　were　good　linear　correlation　in　the　range　of　5-500　ng/L.　Recoveries　were　82%-95%　for　GSM　and　999/-101%　for　MIB,　and　precision　was　5.2%　for　GSM　and　0.8%　for　MIB.　The　limits　of　detection　for　GSM　and　MIB　were　3.　6　and　4.　1　ng/L,　respectively.