In this paper,an octaethylporphyrin film/K+ exchanged glass optical waveguide sensor was fabricated by spin-coating method immobilizing the octaethylporphyrin compound on K+ glass optical waveguide surface.The sensor was used to detect different volatile gases in optical waveguide detection system.Besides,the preparation conditions for the sensor were optimized.The experimental results showed that the sensor has a high sensitivity to methylamine.The detection limit was 1.0×10-8 V/V0(S/N=5.1),and the response time and recovery time was 1.2 s and 2.3 s,respectively.There also existed a good linear relationship for the results obtained in the parallel experiment with the relative standard deviation of 1.1%,which proved the accuracy of the sensor in methylamine gas detection.