Nano-SiO₂ can improve the mechanical properties of cement paste，but it cannot be fully dispersed in cement slurry. Aiming at this problem，a nano sol MCRO-T1 which could be effectively dispersed in cement slurry was prepared using alko-S alkoxysilane as raw material. The effects of MCRO-T1 on the conventional property of cement slurry，mechanical property， permeability and micro morphology of cement paste were studied. Finally，nano sol MCRO-T1 was applied in Bohai Bay. The results showed that the content of solid SiO₂ in MCRO-T1 was 45% and the average particle size was 25 nm. When 1% MCRO-T1 was added，the early strength development time of cement slurry was shortened by 1/3，the compressive strength of cement paste was increased by 62.3%，the flexural strength was increased by 21.4%，and the permeability was reduced by 52.1%. Nano particles filled in the voids inside the cement stone，which increased the compactness of cement stone structure and improved the toughness of cement stone. After MCRO-T1 was applied to the cementing slurry system in Bozhong liner，the early strength of cement stone was effectively improved，the cementing quality was significantly improved，and the problem of formation sealing failure of oil and gas reservoir in Bohai Bay was solved，which was of great significance to the exploration of buried hill gas reservoir in Bohai Bay.