Low-dimensional black phosphorus materials, such as two-dimensional black phosphorus (2D-BP) and black phosphorus quantum dots (BP-QDs), show great potential application value in structural and photoelectric properties. However, they are still faced with problems including uncontrollable synthesis and poor antioxidation performance. In this research, the simple and low-cost synthesis of low-dimensional black phosphorus was achieved by the microwave method. The effects of microwave annealing temperature and annealing time on the structure, morphology, and photoluminescent properties of such black phosphorus were studied. An aluminium oxide (Al₂O₃) protective layer was deposited on the surface of BP-QDs samples through atomic layer deposition, and the influence of Al₂O₃ film thickness on the antioxidation performance of BP-QDs was investigated. The results show that the size of the quantum dots gradually decreases as the microwave annealing temperature rises and the photoluminescence emission peak exhibits blue shift, which demonstrates that the reaction temperature affects the size of the material and then affects the band gap and photoluminescent properties of the material. The black phosphorous nanosheets are gradually peeled off to form BP-QDs as the microwave annealing time increases. The BP-QDs are uniformly distributed and smaller in size when the microwave annealing temperature and time are 250 ℃ and 4 h, respectively. In addition, a thicker Al₂O₃ film offers better protection. Specifically, BP-QDs present the optimal antioxidation performance in the atmosphere when the thickness of the Al₂O₃ film is 20 nm.