Disclosed herein are a fuzzing preprocessing apparatus and method for automating smart network fuzzing. The fuzzing preprocessing method includes collecting communication message samples that are sent by a fuzzing target client to a fuzzing target system, comparing the communication message samples with each other, and then identifying sizes and types of fields of a fuzzing target protocol, determining a property of a protocol field value with reference to ASCII code, determining a coverage of a user field based on a response message to a test communication message that has been sent to the fuzzing target system, and storing a fuzzing protocol data model having a field number, a field type, a field size, a field value property, and a field value of the fuzzing target protocol, as elements.