Abstract: Meso-tetrakis（4-methoxyphenyl）porphyrin（TMP） was used as the sensing material and a K⁺-ion exchanged glass optical waveguide（OWG） was employed as sensing base. The pH value of the porphyrin solution was adjusted by sodium hydroxide and hydrochloric acid. And the porphyrin solutions with different pH fixed on the K⁺-ion exchanged glass optical waveguide surface by spin-coating method to developed the TMP film/K⁺-ion exchanged glass optical waveguide sensors, the gas sensitivity of each prepared sensing element was studied, and the effect of the pH of the TMP solution and the aggregation shape of TMP in the sensor film on the gas-sensitivity of the OWG sensor was investigated. The experimental results reveal that the sensor prepared using a pH=1.00 of TMP solution is very responsive to ehanediamine gas. The sensor prepared using the original solution exhibited an excellent response toward sulfide gases（H₂S, SO₂）.