The new generation avionics network consists of various topologies including point-to-point, arbitrated loop and switched structures. The precise reliability computation of such a large-scale network seems to be an NP-hard problem. According to the reliability analysis and feature of avionic networks, this paper proposed three reliability computation models via topological transformations which are the possible connecting cases of equipment and links in the avionics networks. The proposed models can be applied to compute the reliabilities of point-to-point and arbitrated loop topologies structures precisely, and also the probability of switched topology structure approximately through determining the upper bound. While the approximate reliability calculation process of the avionics system network can be conducted by combining the proposed models for different sub-structures three models. Finally, the approximate reliability analysis of a certain avionic network example is performed with the corresponding result being provided, and then the rules of approximate reliability computing are also indicated. © 2020 IEEE.