A series of triaxial shear tests were carried out on improved low liquid limit clay with different amounts of calcium lignosulfonate (Ca-LS) and different curing time. The law of the stress-strain curve, peak deviator stress and shear strength parameters were analyzed. The internal mechanism of the improved soil was analyzed with the scanning electron microscope. The test results show that Ca-LS can significantly improve the shear strength of clay. With the increase of Ca-LS content, the shear strength of improved soil first increases and then decreases, and the optimal content is 8%. With the increase of curing time, the shear strength of the improved soil becomes stronger, but the strengthening speed gradually slows down. After 7.d of curing, the peak deviator stress of the improved soil containing 8% of Ca-LS is 2 017.23.kPa, which is 236.25% higher than the pure clay that cured for the same time. The cohesion force of the improved soil first increases and then decreases with the Ca-LS content, and the internal friction angle of the improved soil first increases and then remains stable. The internal mechanism of the modified soil strength improvement can be summarized as filling pores, ion exchange, adsorption of wrapped soil particles and cemented soil particle aggregates.