Abstract: In this paper, magnesium potassium phosphate cementitious (MKPC) material was preparaed by adding KH2PO4, dead-burned MgO and borax in a certain proportion to solidify simulated radioactive fluoride liquid waste. The influence of admixtures, such as quartz sand, zeolite, silica fume and fly ash, in the solidified forms was studied. The results show that admixtures don’t change the setting time of the solidified form, but influence its porosity. The porosity increases obviously after adding silica fume and decreases after adding fly ash. After cured 28 d, the compressive strength of the solidified forms is greater than 55 MPa. The loss rate of the compressive strength is proportional to porosity. The solidified forms prepared in this paper have good leaching resistance property. After 42 d leaching test, the leaching rate of simulated nuclides Sr2+, Cs+, Co2+ and the 42 d cumulative leaching rate of simulated nuclide Cs+ are lower than the limit value of GB 14569.1—2011. Average leaching concentration of F- is lower than the limit value of GB 5085.3—2007.