Aluminum formate was used to modify aluminum sulfate based alkali-free liquid accelerator, and the performance index of alkali-free liquid accelerator modified by aluminum formate was tested in this paper. XRD, SEM, TG-DTG and hydration thermal analysis were used to analyze the effect of aluminum sulfate based alkali-free liquid accelerator modified by aluminum formate on the hydration process of cement. The results show that with the increase of aluminum formate content in aluminium sulfate based alkali-free liquid accelerator, the quick setting effect and strength of cement show a trend of increasing first and then decreasing. When the modified content of aluminum formate is 1% (based on the mass percentage of aluminum sulfate), the properties of cement with 8% modified aluminum sulfate based alkali-free liquid accelerator are as follows: initial setting time of 2 min 39 s, final setting time of 5 min 33 s, 1 d compressive strength of 13.2 MPa, 28 d compressive strength of 49.6 MPa, 28 d compressive strength ratio of 114%, and 90 d compressive strength retention rate of 123%, which meets the technical index requirements of the standard “Flash setting admixtures for shotcrete” (GB/T 35159—2017). When the modified content of aluminum formate exceeds 1%, a large amount of AFt inhibits the hydration reaction of C₃S in cement, resulting in the early and late strength reduction.