The invention relates to a wastewater treatment device and a wastewater treatment method thereof. The wastewater treatment device mainly comprises an aerobic expanded bed, an oxygenator, a circulating pump, a feeding pump, a feeding tank, a heating pump, an air pump, a heater and a data control cabinet. According to the invention, by controlling of the rate of circulating water flow, operation of the aerobic expanded bed in an expansion state is realized, so short circuiting water flow is avoided, and organic matter removal loading is improved; a biochemical reaction and oxygen dissolution of the wastewater treatment device are separately completed and independently controlled, so mutual interference of oxygen dissolution and biochemistry performed in a same space in a traditional biochemical process is avoided, and optimization of processes of the biochemical reaction and the oxygen dissolution can be synchronously realized; the aerobic expanded bed and the oxygenator can adopt a high equipment height, and the thickness of a material filling area of the aerobic expanded bed is improved, so the occupied area of a land is reduced, and the efficiency of oxygen dissolution is improved; and the wastewater treatment device has the advantages of less investment, saved occupied land area, high benefits, simple and convenient operation, stable treatment effect, capability of greatly reducing manual labor intensity, and high economic benefits.