avalanche photodiodes （APD） have been fabricated using high quality GaSb-based AlInAsSb quaternary digital alloy grown by molecular beam epitaxy （MBE）. To overcome the tendency towards phase segregation of random alloy， a digital alloy technique with migration-enhanced epitaxy growth method was employed， using a shutter sequence of AlSb， AlAs， AlSb， Sb， In， InAs， In， Sb. The HRXRD curve shows sharp satellite peaks and almost perfect lattice matching. The smooth surface morphology can also be observed on the AFM image. Using optimized digital alloy， AlInAsSb separate absorption， grading， charge， and multiplication （SAGCM） APD was grown and fabricated. At room temperature， the device showed high performance with low dark current density of 0.95 mA/cm² at 95% breakdown and maximum stable gain before breakdown as high as 100， showing the potential for further applications of optoelectronics.