The invention provides a system and a method for improving stability of the oxygen content of oriented electrical steel. The system comprises a steam source, a humidifier and a decompression part, wherein the steam source is connected with one end of the humidifier through a pipeline and is used for providing a water source and a heat source; the other end of the humidifier is connected with a decarburization annealing unit and is used for providing humidifying amount for the decarburization annealing unit; the decompression part is installed on the pipeline between the steam source and the humidifier and is used for controlling the steam pressure to 0.3-0.7MPa; therefore, the steam pressure is stabilized to 0.3-0.7MPa through the decompression part, the humidifying amount and the stability of the oxygen content are further guaranteed, the stability of reaction of a bottom layer is guaranteed, and the appearance and the quality of the oriented electrical steel are improved.