A metal-air fuel cell module includes a cap seat connected detachably to a casing and having a plug portion extending into an inner accommodating space in the casing for plugging an opening in the casing; a conductive gas-diffusion sheet disposed in the casing for covering sealingly air inlets in the casing, and permitting air to pass through; an electrolyte solution filled in the inner accommodating space; a metal sheet disposed in the inner accommodating space and connected detachably to the plug portion of the cap seat; a first electrode plate mounted on the casing, extending into the inner accommodating space and in electrical contact with the gas-diffusion sheet; and a second electrode plate mounted in the cap seat, extending into the inner accommodating space and in electrical contact with the metal sheet.