Some major construction projects require materials that can quickly and easily obtain high mechanical properties. Incorporating early-strength agents is an efficient method to improve the performances of cement with low cost. The authors chose to study Ultra-High Performance Concrete (UHPC) materials based on SulfoAluminate Cement (SAC) at a low water-cement ratio in order to improve the early performance. Set out from this, the author introduced common early-strength agents into SAC to prepare and study the mechanism. Experimental results indicate Ca(HCOO)2 had the best effects on reducing the setting time (Fig.1) and improving the early strength (Fig.2) at the low water-cement ratio. The compressive strength after 4 h reached 41.2 MPa, which was 86.4% higher than that of the blank. The reason was found that Ca(HCOO)2 promoted the hydration ratio in the early stage. Most importantly, unlike other early-strength agents, a new exothermic peak appeared (Fig.3) in the deceleration phase stage after mixing with Ca(HCOO)2. Besides, Ca(HCOO)2 did not change the type of hydration products (Fig.4), but it significantly increased the AFt content (Fig.5, Fig.6) at an early stage.