The invention discloses an aerobic-anoxic biological fluidized bed apparatus, which comprises a biological fluidized bed, an ultrasonic cleaning system and an automatic gas control device, wherein thebottom portion of the biological fluidized bed is connected to the automatic gas control device through a gas inlet pipe so as to provide air, oxygen or nitrogen according to requirements, achieve aerobic-anoxic two-mode operation, perform automatic membrane removing, and achieve the control of the thickness and the biological activity of a biological membrane, and the ultrasonic cleaning systemcan timely clean an effluent filtration screen so as to make the aged biological membrane shed and be discharged out of the system along with the effluent and avoid filler loss. According to the present invention, the aerobic-anoxic biological fluidized bed apparatus has advantages of flexible and stable operation, small occupation area and fast start-up, can treat wastewater with different concentrations, has wide application range, is particularly suitable for the high water-quality change and high water-amount change wastewater caused by the characteristics of rapid product updating and high yield change of Chinese enterprises, and can effectively improve the conditions of high idle rate and high replacement rate of the current environmental protection facilities.