The quality of borehole sealing is a key factor affecting the efficiency of gas production. A new water-rich grouting material (RW) with composite coagulant and other additives was prepared in this study to overcome the disadvantages of long setting time and low stone rate of traditional cement materials. When the coagulants A is 4 g and coagulants B is 2 g, the setting time of RW material was reduced by 60.85% and 50.62%, which significantly shortened the setting time of the RW material, respectively. Based on the orthogonal method, 29 groups of comparative experiments were designed to investigate the interaction mechanism between different additives on the performance index of RW, including setting time, water secretion rate, and compressive strength. Quadratic regression equations were fitted using the response surface method. All the correlation coefficients R2 of each response model were greater than 0.97, R2 and R2adj were less than 0.2 through variance analysis, indicating a high correlation between the actual and prediction results. The water−cement ratio had the most significant effect among all factors on setting time, water secretion rate, and compressive strength of the RW material. The scanning electron microscope (SEM) was used to compared the micromorphological characteristics of RW and conventional Portland cement material (PC). The results showed that the hydration products of RW were mostly smack ettringite, calcium silicate hydrate gel, and calcium hydroxide, which interweaved with each other to form a network structure that was denser than the PC material. Furthermore, the interface bonding degree between RW and injected coal was tighter than that of PC, without obvious cracks at the slurry−coal interface. The results indicate that the addition of composite coagulant can significantly accelerate the hydration process of RW material and also enhance the interface strength of injected coal, which is conducive to improving the grouting quality and sealing effect of the extraction borehole.