An　isotope　dilution　technique　based　on　purge-and-trap　coupled　to　gas　chromatography　with　mass　spectrometric　detection　were　developed　and　optimized　for　the　trace　determination　of　the　typical　odorous　compounds;　Geosmin　(GSM)　and　2-methylisoborneol　(Mm).　The　selection　of　quantitative　ion　and　the　factors　of　programmed　temperature,　the　sample　purge　temperature,　salinity　on　the　extraction　of　odor　compounds　were　discussed.　D-5-Geosmin　and　d(3)-MIB　as　the　isotopes　internal　standards　are　added　to　the　25ml　of　water　sample　containing　sodium　chloride　(20%(m/v)),　and　the　analytes　were　purged　at　60　degrees　C　by　a　flow　of　N-2　in　13min　and　trapped　on　a　Tenax-Silica　Gel-Charcoal　sorbent,　then　separated　and　determined　by　gas　chromatograph　coupled　to　a　mass　spectrometer.　Under　the　optimal　conditons,　the　calibration　curves　of　MIB　and　GSM　were　linear　in　the　range　of　5-500ng/L,　with　a　correlation　coefficient　above　0.9998.　The　limits　of　detection　(LOD)　were　4.12ng/L　for　MIB　and　3.60ng/L　for　GSM.　Recovery　were　82%similar　to　95%　for　GSM　and　99%similar　to　101%　for　MIB,　and　precision　were　5.20%　for　GSM　and　0.78%　for　MIB　at　100ng/L　from　a　reservior　source　water　sample　in　Fuzhou,　China.　This　method　was　applied　to　the　analysis　of　environmental　water　samples　successfully.