A flat fuel cell assembly including a MEA, a cathode porous current collector, an anode porous current collector, a gas barrier material layer, a case, and at least one air baffle is provided. The cathode porous current collector and the anode porous current collector are disposed at two opposite sides of the MEA. The gas barrier material layer is disposed at a side of the cathode porous current collector and has at least one opening for exposing a surface of the cathode porous current collector. The case is disposed at a side of the MEA, the gas barrier material layer is disposed between the case and the MEA, and an air channel is located between the gas barrier material layer and the case. Additionally, the air baffle disposed within the air channel.