The invention provides a methane collector, and a device and a method for measuring methane discharged by a coalbed methane production well. The methane collector comprises a hard top cover, a hard bottom cover, a gas sampling film and hoop rings, wherein the hard top cover is provided with a gas detection hole; the gas sampling film is positioned between the hard top cover and the hard bottom cover in a contracting way and is respectively connected with the hard top cover and the hard bottom cover in a sealing way, so that an expandable space used for collecting coalbed water and the methanecan be formed; the gas sampling film is provided with a sample inlet/a drain outlet through which the coalbed water and the methane can enter and be discharged out of the expandable space; the hoop rings sleeve the outer side of the gas sampling film; one or more hoop rings are available and are closely stuck with the gas sampling film at the outer side of the gas sampling film. The device for measuring the methane discharged by the coalbed methane production well comprises the methane collector. The device and the method can be used for accurately measuring the methane emission of the drain outlet of the coalbed methane production well, thus having important positive significance on improving the accuracy of greenhouse gas verification data of oil and gas industry in China and promoting the work of fighting over climate change.