Abstract: Abstract: Microbial 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, solution tests and sand column tests were carried out by adding 1~30 mmol/L of FeCl3 in the cementing solution. The strengthening effect was evaluated by calcium carbonate generation, unconfined compressive strength and coefficient of permeability. The results show that: (1) FeCl3 can change the morphology and size of calcium carbonate produced by MICP in the solution test. (2) The addition of FeCl3 to the cementing solution can lead to a maximum unconfined compressive strength of up to 1617.9 kPa in sand columns under five injections, which is 10.4 times higher than that of conventional MICP-treated sand columns, and the coefficient of permeability is reduced by two orders of magnitude compared with that of untreated sands. (3) FeCl3 did not increase the amount of MICP calcium carbonate in sandy soils, but modified the distribution pattern of 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.