Abstract: Simulated radioactive spent resins were solidified by sulfoaluminate cement, and the influence of water/binder ratio and the blending amount of naphthalene-based water reducer UNF-5 on fluidity, setting times and compressive strength of waste forms were investigated. With water/binder ratio increasing from 0.25 to 0.35, the fluidity enhances linearly from 228 mm to 280 mm. The initial and final setting time prolong from 3.0 h and 9.3 h to 4.6 h and 10.4 h, respectively. The 28 d compressive strength decreases linearly from 19.8 MPa to 13.5 MPa. When the blending amount of UNF5 increases, the fluidity increases, the setting time decreases initially and then increases, and the compressive strength increases to the maximum and then decreases. With UNF-5 blending amount of 0.05%-0.10%, the fluidity is 200-225 mm, the initial and final setting time are 3.4 h and 11-12 h, respectively, and the 28 d compressive strength is 21.1-21.7 MPa.