Abstract: The mud replacement of freezing hole has become a necessary part of freezing shaft sinking in rock strata, but in the lowering process, the freezing pipe is prone to excessive slurry viscosity resistance, and even be locked, leading to borehole failure. In order to deeply understand the performance deterioration law of cement slurry and its mixture in deep hole environment, the laboratory tests of retarded cement slurry and mixed slurry are carried out respectively, taking the apparent viscosity as the measurement index and considering the factors such as curing time, temperature, water loss state and volume ratio of mixed slurry. The results show that the viscosity of the cement slurry and mixed slurry increases with the extension of curing time, but the viscosity value and growth rate of the mixed slurry are much higher than those of the cement slurry within 20 h of curing time. The viscosity of the both has a nonlinear relationship with temperature. And the viscosity growth of slurry is accelerated by water loss state, especially the viscosity of the mixed slurry. The viscosity and volume ratio of the mixed slurry show a non-linear relationship. Compared with the retarded cement slurry, the viscosity of the mixed slurry increases sharply which is more affected by curing time, temperature and water loss state. The analysis shows that the sudden increase of viscosity and the sharp decrease or even loss of the fluidity of the mixed slurry are the key reasons for the excessive sinking resistance and even the locked freezing pipe. Therefore, controlling the height of the slurry mixing section and inhibiting the viscosity growth of the mixed slurry are the key to ensure the safe and smooth sinking of the freezing pipe.