In order to explore the physical and mechanical properties of weak expansive soil improved by urease Enzyme-Induced Calcium Carbonate Precipitation (EICP) technique, the expansion characteristics and mechanical properties of weak expansive soil treated by EICP were tested by soybean urease. The effects of urease concentration, initial Ca²⁺ concentration, enzyme-binder ratio, urine-calcium ratio and curing time on the formation rate of calcium carbonate and free expansion rate were studied by orthogonal test of EICP multi-factor ratio, and the optimum ratio of EICP reaction solution was determined. On this basis, the expansive soil was improved by different dosages of EICP reaction liquid, and the effect was tested by free expansion rate test, unconfined compressive strength test and triaxial compression test. The results show that when the content of EICP reaction solution is 20%, the inhibiting is the best, and the mechanical strength and calcium carbonate formation rate of soil are the highest. The precipitate induced by soybean urease is calcite calcium carbonate, which is attached to the surface of soil particles. It not only fills the pores of soil particles, but also cements the skeleton particles of soil, hinders the contact between soil and water, improves the compactness and bonding strength of soil, and finally improves the expansibility and mechanical properties of expansive soil.