In order to improve the effects of cement and fly ash on the solidification of waste soft clay with high water content, sodium silicate and quick lime were selected as additive and dispersing agent, respectively. The unconfined compressive strength test (UCS), X-ray diffraction (XRD), and scanning electron microscope (SEM) were used to research the influences of mixing ratio and age on the water stability, strength behavior, solidification mechanism of solidified waste soft clay. The results show that 3% (mass fraction) cement combined with 7% (mass fraction) fly ash, 2% (mass fraction) quick lime and 2% (mass fraction) sodium silicate significantly improve the strength and water stability of solidified soft clay. The strength of solidified soft clay reaches 1 MPa, and meets the strength requirements of the cement-fly ash base layer. With the same mixing ratio of cement, fly ash and water glass, the mass fraction of quick lime increases from 0% to 2%, and its strength increases about 375 kPa. Adding the quick lime is conducive to the uniform mixing of the other curing agents. It indicates that the water absorption and dispersion effect of quick lime play a vital role in the solidified soil. In addition, SEM images show that after adding the composite curing agent, the large aggregates disappear, a large number of sheet structures generate, the large pores between the particles are filled, and the strength of soft soil is also improved.