The effects of P/Al ratio and Cr/Al ratio on the phase composition, microstructure, mechanical properties and dielectric properties of quartz fiber-reinforced phosphate composites were investigated. The results show that the phase composition of the phosphate matrix is mainly composed of Berlinite phase, low-temperature quartz type AlPO₄ and  unreacted α–Al₂O₃, and the composition ratio and microstructure of the matrix phase are influenced by the P/Al ratio and Cr/P ratio. When P/Al=4.1 and Cr/P=0.04, the composites have the best mechanical properties, with tensile strength of 108.6 MPa, bending strength of 135.3 MPa and fracture toughness K_ⅠC of 6.6 MPa·m^1/2, and the composites exhibit the plastic fracture characteristics of weak bonding interface. It is analyzed that at this time the matrix contains more Al(H₂PO₄)₃ phase with good bonding properties, and the matrix exhibits a smooth planar-like structure, which is conducive to the formation of a complete and continuous good interfacial layer between the matrix and the fiber. In addition, the dielectric properties of the materials are greatly affected by the Cr content, except for Cr/P=0.08 materials, the dielectric properties of the prepared materials can meet the performance requirements of high-temperature wave-transparent materials, and have a broad application prospect.