Abstract: In the paper, a new general optimal design method of stable high-order interpolative - A/D modulator is presented. The design principle and process in detail are given by using an interpolative structure in state space and the transfer function conversion, then the noise transfer function is realized by optimized zero and Butterworth poles. The stable condition of modulator is studied and the structure coefficients are gained by minimizing the state energy in order to make the modulator more stable. Finally illustrative examples are demonstrated to show the effectiveness.