Magnesium potassium phosphate cement (MKPC) is susceptible to high-temperature damage when used as a fireproofing coating or structural repair material and as a nuclear waste encapsulation shell, and the strength loss and dimensional shrinkage at about 100 °C severely limit the application of MKPC. Therefore, in this paper, the macroscopic properties, physical phase composition and microscopic morphology of sucrose-modified MKPC at room and high temperatures (20°C, 50°C, 120°C) are investigated from the perspective of modified retarder, and the mechanism of sucrose's influence on MKPC at high temperatures and the optimal dosage are speculated, and the Pearson correlation analysis is performed on the various macroscopic and microscopic indexes. The results showed that 2.5 % sucrose doping could reduce dimensional shrinkage by 59.6 % and increase late strength by 21.8 % at high temperatures, significantly optimizing the macroscopic properties of MKPC. The inhibition of the high-temperature decomposition product MgKPO4·H2O by sucrose and the reduction of pores formed by water evaporation are among the main reasons for the optimization of the properties. Additionally, the adsorption of amorphous products to form new polymers that fill the pores is also an important reason for the optimization of performance. However, Pearson's correlation analysis showed that too much sucrose contributed to the reduction of pulp strength, and its optimal dosage should be between 2 % and 3 %.