An　approach　is　proposed　for　quality　(Q)　factor　estimation　from　the　variation　of　envelope　peak　instantaneous　frequency　(EPIF).　For　a　frequency-independent　Q　model,　assuming　that　the　propagating　wavelet　can　be　modeled　by　a　Gaussian　function　with　constant　phase,　an　approximate　analytic　relation　between　Q　and　EPIF　variation　is　derived.　Synthetic　tests　show　that　the　EPIF　method　has　higher　resolution　and　is　less　sensitive　to　noise　and　interference　reflection　than　common　methods.　The　field　test　of　reflection　seismic　data　indicates　that　the　zone　of　lower　Q-factors　corresponds　well　to　the　gas　reservoir.