A fingerprint image processing method, applied in an optical fingerprint identification system of an electronic device, wherein the electronic device comprises a display panel, the display panel comprises a display pixel array, the optical fingerprint identification system comprises an image sensing array, the image sensing array is disposed under the display pixel array, characterized in that, the fingerprint image processing method comprises: obtaining a first background image and obtaining at least an interfering frequency (f I,1 -f I,N) when the display panel is not pressed by a finger of a user, wherein the step of obtaining the at least an interfering frequency comprises: obtaining a second background image, wherein no fingerprint image is included in the first background image and the second background image; performing a subtracting operation and a transforming operation on the first background image and the second background image, to obtain a difference image spectrum (Diff_IM_SPM), wherein the transformation operation is a Fast Fourier Transform; and performing an energy detection operation on the difference image spectrum, to derive the at least an interfering frequency from energy spectrum of the difference image spectrum; receiving a received image when the display panel is pressed by the finger of the user; performing a subtracting operation on the received image and the first background image, to obtain a difference image; and performing a filtering operation on the difference image at the at least an interfering frequency to filter out the interference, to obtain an operational result; wherein the optical fingerprint identification system determines a fingerprint within the received image according to the operational result. obtaining a first background image and obtaining at least an interfering frequency (f I,1 -f I,N) when the display panel is not pressed by a finger of a user, wherein the step of obtaining the at least an interfering frequency comprises: obtaining a second background image, wherein no fingerprint image is included in the first background image and the second background image; performing a subtracting operation and a transforming operation on the first background image and the second background image, to obtain a difference image spectrum (Diff_IM_SPM), wherein the transformation operation is a Fast Fourier Transform; and performing an energy detection operation on the difference image spectrum, to derive the at least an interfering frequency from energy spectrum of the difference image spectrum; obtaining a second background image, wherein no fingerprint image is included in the first background image and the second background image; performing a subtracting operation and a transforming operation on the first background image and the second background image, to obtain a difference image spectrum (Diff_IM_SPM), wherein the transformation operation is a Fast Fourier Transform; and performing an energy detection operation on the difference image spectrum, to derive the at least an interfering frequency from energy spectrum of the difference image spectrum; receiving a received image when the display panel is pressed by the finger of the user; performing a subtracting operation on the received image and the first background image, to obtain a difference image; and performing a filtering operation on the difference image at the at least an interfering frequency to filter out the interference, to obtain an operational result; wherein the optical fingerprint identification system determines a fingerprint within the received image according to the operational result.