The invention provides a bonding agent for stemming and a preparation method thereof. The method comprises the following steps of: synthesizing A-stage phenolic resin and mixing the A-stage phenolic resin with a first organic solvent to obtain A-stage phenolic resin solution; synthesizing linear phenolic resin, mixing the linear phenolic resin with a second organic solvent to obtain linear phenolic resin solution; uniformly mixing the A-stage phenolic resin solution with the linear phenolic resin solution to obtain the bonding agent for the stemming; and the mass ratio of the A-stage phenolic resin and the linear phenolic resin in the bonding agent for the stemming is (2-50):(50-98). The bonding agent has the beneficial effects that the linear phenolic resin is adopted as the resin component of the bonding agent; the A-stage phenolic resin is adopted as the component of a curing agent; the curing rate is slower and is about 10-20 minutes; as the mobility of the stemming at a high temperature is beneficial to being improved through reducing the curing rate, the stemming is not easily blocked in a mud gun; and meanwhile, the storage condition of the bonding agent is also greatly reduced so as to be beneficial to prolonging the quality guarantee period of the bonding agent.