Aiming at the defects and shortcomings of the present microwave expansion device for tobacco stem, we developed a steam microwave synergistic expansion equipment. The equipment was mainly composed of material transferring system, microwave system, steam circulation system and heating chamber, using steam and microwave as compound heating energy, and resulted in reducing the microwave power and obtaining high expansion degree. That gave full played to the quality advantages of microwave expansion, and effectively prevented the occurrence of microwave ignition phenomenon. Compared with pure microwave expansion equipment, the expansion degree for tobacco stem had an average increase of 578%; the effective expansion rate had an average increase of 406%; the full value for obtained stem wire had an average increase of 0.46 cm³/g; the whole wire rate had an average increase of 2.03% and broken silk rate had an average decrease of 0.95%. Sensory quality got a significant improvement.