 Filtering is an application that is performed on signals whenever certain frequencies are to be removed so as to suppress interfering signals and reduce background noise.A mixed filter is a kind of filter that is different from the traditional Finite Impulse Response(FIR) and Infinite impulse response(IIR) filters and these three filters are explained here in detail.We can combine the M-D Discrete Fourier transform(DFT) method and the M-D linear difference equation(LDE) method to filter the M-D signals.