To study the mechanism of using nickel-iron slag powder as a solidification material for cement soil, the microscopic properties of nickel-iron slag powder cement soil were deeply studied to more accurately reveal the physical and chemical changes during the solidification process. The size distribution of nickel-iron slag powder and cement was analyzed by laser particle size test, and it was found that the dispersion and average particle size of nickel-iron slag powder were slightly smaller than that of cement. The internal structure of nickel-iron slag powder cement soil was studied by synchronous thermal analysis experiment, which showed that nickel-iron slag powder filled the pores of cement soil, improved the degree of intergranular bonding, and thus improved its compressive strength. The microscopic experiment by scanning electron microscope (SEM) showed that a moderate amount of nickel-iron slag powder was beneficial to enhance the dynamic and static strength of cement soil, and the strength of cement soil also increased further with the increase of curing age.