Abstract: This paper presents the all-phase filter design methods based on two kinds of symmetric frequency sampling. Under the condition of no window and single window, it is proved that the all-phase transfer curves designed by conventional symmetry frequency vector and even symmetry frequency vector can pass through the frequency sampling points of odd multiples and even multiples of /N, respectively. In this way all-phase filter can control critical frequency to a relatively precise extent. Simulation experiment proves that the performances of these two kinds of all-phase filter are superior to that of filter designed by neural network methods.