According to the features of soil solidification, a series of unconfined compression and water stability tests is conducted to investigate the effects of the variation of potassium salt and phosphate concentrations on the early strength of sulphoaluminate cement-stabilized soil. X-ray diffraction (XRD) analysis of phase composition of the stabilized soil is performed to reveal the mechanism for the changes of the early strength of the stabilized soil. The experimental results show that there is a threshold of about 0.6% in potassium salt and phosphate contents. If the mixing amount of the salts in the stabilized soil is lower than this threshold value, the strength of the stabilized soil increases with the increase of the salt concentration; while the amount exceeds the threshold, the strength of the stabilized soil will decrease. If the salt concentration is not more than 2%, the water stability of the stabilized soil with salt is similar to that without salt; the softening coefficient of the stabilized soils after 7-day curing is larger than 70%, whereas the water stability of the stabilized soil with K2SO4 is poorer, and the softening coefficient is about 60%. XRD analysis shows that the generation of insoluble mineral crystal with high strength and expansibility is the main reason that the early strength of the stabilized soil is improved after introducing potassium salt or phosphate. If the salt concentration is too high, the early strength of stabilized soil will be drastically reduced due to mineral crystal excessive expansion effect, which destroys the structure of stabilized soil .