Abstract: Due to its excellent chemical stability, irradiation resistance, and thermal stability, strontium zirconium phosphate (Sr_0.5Zr₂(PO₄)₃) could be used to immobilize fission product strontium (Sr). In addition, monazite (LnPO₄) is known as a phosphate mineral that can persist for a long time in nature. From a structural perspective, the LnPO₄ polyhedron of monazite could immobilize a wide variety of radionuclides (Sm, Eu, Gd, U, etc.) according to the principle of isomorphism and there is no change to the crystalline structure. It is regarded as an ideal host matrix for minor actinides because of high performance in mechanical stability, chemical stability, and irradiation tolerance. Therefore, in this study, (1−x)Sr_0.5Zr₂(PO₄)₃-x(Sm_0.5Eu_0.5)PO₄ (SrZP-monazite, x=0.0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0) phosphate composite ceramic waste forms, where ⁹⁰Sr and trivalent minor actinides were simulated by ⁸⁸Sr and Sm³⁺/Eu³⁺ respectively, were obtained via in-situ one-step microwave sintering. XRD, SEM, FTIR and PCT tests were conducted to systematically explore the density, structural evolution and chemical stability of SrZP-monazite series composite ceramics. According to the experimental results, the optimal sintering conditions for the SrZP-monazite series composite ceramics were sintered at 1 100 ℃ for 1.5 h. Under this condition, the prepared samples are found to be dense with a maximum relative density of 97.5%. The prepared SrZP-monazite composite ceramics are only composed of SrZP phase and (Sm, Eu)PO₄ phase, which are uniform in grain distribution. The change in x value causes no obvious changes to cell parameters, indicating a limited effect of the biphasic ratio changes on the phase structure of the composite ceramics. As revealed by the results of PCT, the SrZP-monazite (x=0.5) sample exhibits high chemical stability, and multiphase ceramics outperforms single-phase ceramics in leaching resistance, with the normalized leaching rates of all elements being at relatively low magnitudes (Sr: about 10⁻⁴ g·m⁻²·d⁻¹; Sm/Eu: 10⁻⁵-10⁻⁶ g·m⁻²·d⁻¹). In conclusion, SrZP-monazite composite ceramic waste forms are successfully prepared by microwave one-step. The samples achieve highly efficient co-immobilization of fission products (Sr) and trivalent minor actinides and high waste loading, while the microwave-assisted heating mechanism significantly shortens the sintering cycle and enhances material densification. And the SrZP-monazite (x=0.5) composite ceramics perform well in chemical stability.