Abstract: The microbially induced calcium carbonate precipitation (MICP) is a promising technique for soil improvement. However, the disadvantage of the MICP-based method for soil treatment is that the intended effect of improvement can only be achieved by multiple treatments of the cementing solution. To enhance the efficiency of soil treatment by microbial mineralization, the solution tests and sand column tests are carried out by adding 1~30 mmol/L of \mathsfFeCl_3 in the cementing solution. The strengthening effect is evaluated by the calcium carbonate generation, unconfined compressive strength and coefficient of permeability. The results show that: (1) \mathsfFeCl_3 can change the morphology and size of the calcium carbonate produced by the MICP in the solution tests. (2) The addition of \mathsfFeCl_3 to the cementing solution can lead to a maximum unconfined compression strength of up to 1617.9 kPa in sand columns under five injections, which is 10.4 times higher than that of the conventional MICP-treated sand columns, and the coefficient of permeability is reduced by two orders of magnitude compared with that of the untreated sands. (3) \mathsfFeCl_3 does not increase the amount of the MICP calcium carbonate in sandy soils, but modifies the distribution pattern of the calcium carbonate in the pores of the sandy soils, thus increasing the strength of sandy soils and lowering the coefficient of permeability of sandy soils in co-operation with the MICP.