Abstract: The optimized design of X-ray spectrum filter for computed tomography is studied by Monte Carlo method in this paper. The generation process of X-ray using electron bombardment metal target and the transport process of X-ray through different filters were simulated by EGSnrc software. The formula for optimized design was presented on the basis of signal to noise ratio (SNR). The results show that the optimal parameter for filter design exists, and it is different under different imaging conditions and requirements, which is determined by the actual conditions.