In this paper, a novel bonding method for microfluidic devices was presented. The organic solvent fumigation bonding method can be used to produce multi-layer PMMA microfluidic devices under the condition of room temperature and low pressure. During the bonding, we choose chloroform as bonding solvents, the polyimide tape was used to protect no-need-bonding side of the cover sheet and the sealant silicone adhesive was used to protect the microstructure in the bonding side. The substrate was fumigated for 5minutes in the saturated steam conditions, then remove the polyimide tape as well as the sealant silicone adhesive. Assemble the fumigation cover sheet to the substrate with microchannel by using fixtures, soon after put the fixture and the substrates into the oven, dried at 50 °C for 10 minutes. Finally, remove the fixture, the bonding complete. Because of the bonding was accomplished under conditions of low temperature and pressure, the deformation of microchannel is very small. When the method was used for multilayer chip bonding, it also achieved good results.