The invention discloses a device and method for performing modal testing on an inflatable flexible film structure based on a hammering excitation method. A force hammer is used for knocking a marked excitation point of the inflatable flexible film structure so as to apply vibrational excitation, a force sensor installed on the force hammer receives force signals, and an acceleration sensor installed on the surface of the inflatable flexible film structure receives acceleration signals; after the force signals and the acceleration signals are amplified by a charge amplifier, a data acquisition instrument inputs received acceleration electrical signals and force electrical signals into a computer, the computer performs digital-to-analogue conversion on the signals and obtains a frequency response function matrix according to the force signals and the acceleration signals, and finally modal vibration shapes of all orders and related modal parameters of the structure are obtained through parameter identification. Thus, modal numerical simulation of the inflatable flexible film structure can be verified and provided with reference. The device is simple in structure, convenient to operate and wide in application range.