Abstract: Microbial induced calcium carbonate precipitation ( MICP) is a new in situ grouting technology． It can improve the flow characteristics of liquefiable sandy soil through microbial and calcium salt reaction and become calcium carbonate precipitation． Ammonium ( NH4 + ) ，as an important factor of characterizing CaCO3 crystallizing process，can fully reflect the effect of treatment on liquefiable sand． In this paper，aerobic Sporosarcina pasteurii was used，the mixed solution ( urea and three calcium salts solution) was selected as bacteria solution and nutritive salt solution respectively，and NH4 + characterization on microbial solidification process was also studied． The results showed that changes of NH4 + concentration could characterize the effect of MICP on liquefiable sand improvement． Among Ca( CH3COO) 2 ，Ca ( NO3 ) 2 and CaCl2 solution，the former was the best． The amount of nutrient salt consumption also significantly improved the solidification effect of liquefied sand，which was verified by the estimated permeability of samples and ultrasonic experiments after solidification．