The invention provides a steam channeling blocking agent. The steam channeling blocking agent includes a gelling agent, a crosslinking agent, a stabilizer and water. The gelling agent used in the above steam channeling blocking agent is modified sulfonated phenolic resin, the modified sulfonated phenolic resin is obtained by reacting sulfonated phenolic resin with an organic amine, almost no molecular degradation exists at a high temperature of 250 DEG C, the modified sulfonated phenolic resin is in combination with the cross-linking agent for use, so that the modified sulfonated phenolic resin can be deeply cross-linked to form a reticulated macromolecular gel with high blocking strength and good high-temperature resistance, and the high-temperature resistance and blocking performance ofthe steam channeling blocking agent are significantly improved; the added water can adjust the fluidity of the gel, and the added stabilizer can facilitate great improving of the strength and stability of the channeling blocking agent under high-temperature conditions, thereby facilitating improving of the effective blocking time and blocking effect; and in addition, the steam channeling blockingagent prepared by using the above components has the advantages of low costs and a simple preparation process.