The soft soil in the coastal region of South China is taken as the research object, and the slag/fly ash activated by sodium silicate is used to solidify it. Results show that the single-doped slag or fly ash has a limited effect on enhancing the strength of silt soft soil. However, with a 28-day curing age, the strength of solidified soil increases with slag content but decreases with the increase in fly ash content. Incorporating sodium silicate significantly affects the strength of the solidified soil, with reinforced soil strength gradually rising with the sodium silicate content. The maximum strength achieved by solidifying the soft soil sample with slag activated by sodium silicate reaches 850 kPa, 2.55 times higher than that of single-doped slag. The optimal sodium silicate content for samples with 5 % and 10 % and 15 % and 20 % slag content are 4 % and 3 %, respectively. Similarly, the maximum strength obtained by solidifying the soft soil sample with fly ash activated by sodium silicate is 483 kPa, 1.71 times higher than that of single-doped fly ash. The optimal sodium silicate content for samples with 5 % and 10 % and 15 % and 20 % fly ash is 3 % and 4 %, respectively. Furthermore, the solidification effect of sodium silicate-activated slag on soft soil is superior to that of sodium silicate-activated fly ash. Microscopic testing reveals the formation of cementing material within the solidified soil, binding the soil particles together. This cementing material corresponds to the hydration product C-(A)-S-H. Due to the higher alkali activity of slag compared to fly ash, it generates a greater amount of C-(A)-S-H hydration cementitious material, filling the pores and enhancing the cementation between soil particles, thereby improving the strength of the solidified soil. Consequently, the solidification effect is enhanced.