In this paper, tetraphenylporphyrin cobalt was synthesized via Alder method, achieving the detection of ethanol. Using the means of NMR (1H-NMR), Field-Emission Scanning Electron Microscope (FE-SEM), Infrared (IR), and Ultraviolet (UV-vis) to characterize. We successfully prepared tetraphenylporphyrin cobalt thin film /K exchanged glass waveguide sensing element, that uses tetraphenylporphyrin cobalt as sensitive reagent, by the method of spin coating to detect a variety of gases. The detection results show that the gas sensing element of ethanol have a good selective response, high sensitivity, the response time and recovery time were 1.5 s and 13s respectively, signal to noise ratio S/N = 4.857, RSD = 0.8% (V/V0 = 1?0-4). In parallel experiment, the results have a good linear relationship (R=0.9924), that proved the accuracy of the sensor element to ethanol gas detection.