The invention relates to a combustible gas leakage alarm, belonging to the field of combustible gas safety detection. A combustible gas sensor can be used for detecting the gas leakage, and the detection results are converted into the change of voltage. Then, an acoustic, optical and electric warning circuit can be controlled by a comparison circuit, an amplitude limiting circuit, etc. When gas leakage occurs, the user is prompted by the combustible gas leakage alarm to take measures, so that accident is prevented. According to the service condition, threshold can be flexibly set and adjusted, thus being higher in accuracy.