The invention discloses an automatic adding system for an anti-blocking agent for a compound fertilizer, wherein an oil storage tank is connected to a heating tank through a transfer pipeline, the bottom part of the heating tank is provided with an oil weighing sensor, the lower part of the heating tank is communicated with a hopper of a conveyer through an oil transfer pipe, a metering pump is arranged on the oil transfer pipe, the metering pump is driven by a variable frequency motor, the outlet of the conveyer is arranged in an enveloping machine, the conveyer is driven by the variable frequency motor, a fertilizer metering conveyer belt is provided with a fertilizer weighing sensor, a fertilizer conveying tank is arranged below an outlet end of the fertilizer metering conveyer belt, an outlet of the fertilizer conveying tank is arranged in the enveloping machine, and a PLC (programmable logic controller) is electrically connected with a touch screen; the fertilizer weighing sensor, the oil weighing sensor, the metering pump variable frequency motor and the conveyer variable frequency motor are electrically connected to the PLC, respectively. The automatic adding system is simple in structure and convenient to operate, the added amount of the anti-blocking agent is exact, the labor intensity of the workers is reduced, the production cost is reduced, and the anti-blocking property of the compound fertilizer is effectively improved.