Abstract: Understanding the kinetics and viscosity of hydrate slurry in gas-water-sand system is of great significance for the high-efficiency and high-safety development of natural gas hydrates. The effect of micron-sized sands with various concentrations and particle sizes on the hydrate formation, dissociation, and viscosity in gas-water-sand system are investigated in this work. The experimental results show that the hydrate induction time in the sandy system is slightly prolonged compared to the pure gas-water system, and the inhibition effect first strengthens and then weakens as the sand concentration increases from 0 wt% to 5 wt%. Besides, the difference of hydrate formation amount in various cases is not obvious. The concentration and particle size of sand have little effect on the kinetics of hydrate formation. Both promoting and inhibiting effects on hydrate formation have been found in the sandy multiphase fluid. For the viscosity characteristics, there are three variations of hydrate slurry viscosity during the formation process: Steep drop type, S-type and Fluctuation type. Moreover, appropriate sand size is helpful to reduce the randomness of slurry viscosity change. Meanwhile, even at the same hydrate volume fraction, the slurry viscosity in the formation process is significantly higher than that in dissociation process, which needs further research. This work provides further insights of hydrate formation, dissociation, and viscosity in gas-water-sand system, which is of great significance for safe and economic development of natural gas hydrates.