Alumina fiber reinforced ceramic matrix composites are characterized by good mechanical properties, high temperature oxidation resistance, corrosion resistance and excellent dielectric properties. This material can be used as a kind of high temperature-resistant wave-transmitting functional material for radome. Taking Al2O3 and mullite slurry as basement, Al2O3 fiber as reinforcement, and LaPO4 as interface, Al2O3/Al2O3 composite is fabricated by repeating infiltration and high temperature treatment process. And then, the tensile strength of the composites at room temperature and 1 200 ℃ are measured, and the SEM is employed in observing the fracture microstructure. The tensile strength of Al2O3/Al2O3 composites with LaPO4 interface at room temperature is 148.3 MPa, and increment of tensile strength is 20.1% in comparison with Al2O3/Al2O3 composites without interface. The tensile strength of Al2O3/Al2O3 composites with LaPO4 interface at 1 200 ℃ is 129.6 MPa, and its increment is 24.9% in comparison with Al2O3/Al2O3 composites without LaPO4 interface. The SEM observation shows that the fracture surface of the composite without LaPO4 interface is smooth at crack, and brittle in fracture. A large number of fibers are pulled out in the fracture of alumina fiber reinforced ceramic matrix composites with LaPO4 interface phase, showing ductile fracture characteristics. The average dielectric constant of the composite material is 5.77 and the dielectric loss is 0.001 8 when the frequency is 10 GHz and RT; the average dielectric constant of the material at 1 300 ℃ is 6.18 with the dielectric loss is 0.002 0. The change rate of electric constant and dielectric loss is 7.10% and 11.1% respectively, meeting the needs of change rate <15%, and such a material is expected to be used in the field of wave-transparent composite materials.