A method to enhance the adherence of Al2O3 coating with AISI 316L metallic substrate was proposed in this study. The substrate was aluminized by pack cementation at 850°C for 10 h, and then oxidized at 900°C for 10 h, subsequently, the Al2O3 whiskers formed uniformly. The suspension mixing 3 μm γ-Al2O3 powder, alumina sol, PVA and water was directly applied to the microchannels pretreated by above mentioned aluminizing and oxidation method by dip coating. And then the sample was dried and calcined at 600°C for 2 h to form γ-Al2O3 coating in the micochannel. The morphology and phase composition of the coating were characterized by X-Ray diffraction (XRD), energy dispersive spectrometer (EDS), scanning electron microscope (SEM). The adhesion between the substrate and coating was tested by ultrasonic vibration. The results showed that aluminized treatment could effectively improve the adhesion, and the mass-loss rate of the coating was only 1.24%. The main pore size of the coating was between 30 Å and 100 Å. The coating has no cracks, and possessed with high specific surface area, 234 m2/g.