The invention provides a network Smurf attack characteristic instant defense circuit realization method based on an FPGA (field programmable gate array). A defense circuit is arranged between a data link layer and a data physical layer of an Ethernet interface, and is connected with an MAC (multiple access channel) and a PHY (physical layer) through an MII (medium independent interface) respectively; the method includes the following steps: A, the defense circuit is started after a message sending signal or a message receiving signal is received by the MII; B, fields of network data frames are distributed by a half-byte counter controller to a register for latching; C, numerical values of the register and the characteristic numerical value codes are compared by a numerical value comparator; D, a combinational logic circuit controls an FIFO (first in and first out) cache module circuit to discard or process network data frames. Compared with the prior art, the network Smurf attack characteristic instant defense circuit realization method based on the FPGA, provided by the invention, has the advantages of pure hardware implementation, high real-time performance, high flexibility, no occupation of CPU and actual bandwidth of internet access, as well as higher stability.