Expanding the extra high voltage AC/DC hybrid transmission system and improving the transfer capability of the network are the primary tasks of the power network in China. With the increasing expansion of AC/DC transmission system scale, the super large scale hybrid network has taken shape in china, then the systematic research on ATC calculation model and algorithm for AC/DC systems is urgently needed. A new ATC computation model for AC/DC hybrid transmission system is proposed in this paper. In this model the effect of multiterminal DC system can be considered. CPF algorithm is presented to solve this model, then the ATC value of AC/DC hybrid transmission system can be gained. The algorithm based on MATLAB6.5 is developed. IEEE 14-bus test system is used to verify the presented approach.