Metakaolin was introduced into the hydrated magnesium silicate cement and the compressive strength and pH value of the hydrated magnesium silicate cement were measured.The phase and microstructure of the hydrated magnesium silicate cement mixed with metakaolin were analyzed. The results show that the compressive strength of the magnesium silicate hydrate can be improved by adding less than 10% metakaolin， and the compressive strength of the magnesium silicate hydrate can be increased by 60.9% when 8% metakaolin is added. Al₂O₃ in metakaolin participates in the reaction， which leads to the increase of hydration degree of the system. The hydration degree is the largest when the content of metakaolin is 8% and the mass loss is 3.08%，which is higher than that of the blank group. The pH value of the hydrated magnesium silicate cement system is increased by metakaolin， and the amount of silica fume dissolved decreases with the increase of the content of metakaolin， which affects the formation of hydrated magnesium silicate.