The invention discloses a clay shielding agent and a preparation method thereof.The clay shielding agent is prepared from, by weight, 15-25 parts of sodium silicate, 5-15 parts of potassium trimethylsilanolate, 10-20 parts of sodium tripolyphosphate, 1-5 parts of organic acid salt, 1-5 parts of sodium alkyl sulfate and 30-40 parts of water.The organic acid salt is prepared from 40-60 wt% of sodium humate and 40-60 wt% of zinc gluconate.According to the clay shielding agent, proper sodium alkyl sulfate and organic acid salt are selected, and therefore adverse impacts of clay can be effectively shielded; the clay in concrete gravel materials is preferably adsorbed to improve the effect of a polycarboxylate superplasticizer; the raw material source is wide, chemical reactive synthesis is not needed, and the preparation method is simple, remarkable in effect and suitable for industrial mass production.