The invention discloses an anti-caking agent for a powdery chemical fertilizer. The anti-caking agent for the powdery chemical fertilizer is prepared from oyster shell micro powder, talcum powder and an anionic surfactant. The anti-caking agent for the powdery chemical fertilizer comprises the following chemical components in percent by mass: 30-65% of calcium carbonate, 0.5-3.5% of stearic acid, 0.5-4.5% of sodium dodecyl benzene sulfonate, 15-35% of silicon dioxide, 10-20% of magnesium oxide and 5-10% of calcium oxide. The anti-caking agent for the powdery chemical fertilizer has strong adsorbability and good anti-caking property, is easy to be degraded, non-pollution, convenient to use and low in usage amount, is rich in nutrient elements, such as calcium and magnesium, required by crop growth, can be combined with an oily anti-caking agent to be applied, especially has a more obvious effect on a high-nutrient chemical fertilizer, and is lower in comprehensive cost; a main ingredient oyster shell is available and cheap, has a nano micropore structure, contains multiple amino acids and trace elements, and also has the effect of alleviating soil hardening.