In order to develop alternative materials of hydraulic lime and enhance the improvement effect of traditional calcareous soil in the restoration of earthen sites, the soil samples with different contents of hydraulic lime, lime and metakaolin were prepared by taking typical silty soil in Henan province as the research object. The unconfined compressive strength test was conducted after curing to a predetermined age. Meanwhile, some soil samples were tested by SEM and XRD and compared with hydraulic lime soil. The results show that with the increase of metakaolin content, the failure strain of limestone soil increases and the unconfined compressive strength increases significantly, but the strength growth rate increases first and then decreases with the peak value at metakaolin content 4%. When the curing period increased from 7d to 28d, the strength increase of lime-metakaolin soil was significantly higher than that of lime soil. Considering the failure strain, unconfined compressive strength, strength growth rate and the strength requirements of European standard BS. En459-2015 on NHL2 (2 ~ 5MPa), 6% lime + 4% metakaolin and 8% lime + 4% metakaolin can effectively replace 8% and 10% hydraulic lime. Combined with the SEM and XRD test results, the hydration products (C4AH13, CSH, etc.) formed after metakaolin incorporation join the soil particles and fill the pores, making the improved soil have a certain degree of hydraulicity and more compact microstructure.