Abstract: The cement mortar fixed formula of super compressed pieces of medium and low level radioactive solid waste in 2 m³ waste packaging box was studied. At present, the fixed formula of 82.5# high-strength sulfoaluminate cement mortar has been applied in industry. Due to the shortcomings of 82.5# high-strength sulfoaluminate cement, such as high price, few manufacturers, early strength and concentrated heat release, the cementation raw material was replaced by 82.5# high-strength sulfoaluminate cement with 42.5# ordinary portland cement. The influence of a series of parameters such as water-cement ratio, ash-sand ratio, sand gradation and additive amount on the fluidity, compressive strength(28 d) and chloride penetration resistance(28 d) of the cement fixator was verified through experiments. The results show that the fluidity of the cement fixator samples in a reasonable formulation range is 310-335 mm. The compressive strength(28 d) is 82.1-86.0 MPa, and the chloride penetration resistance(28 d) is 756-1 192 C, both of which meet the requirements of the nuclear industry standard(EJ1186-2005).