The invention provides a re-optimizing method and system for unmanned-aerial-vehicle formation communication topology based on a minimum arborescence. The re-optimizing method and system are used for optimizing reconstructed unmanned-aerial-vehicle formation communication topology after communication failure of an unmanned aerial vehicle in a formation appears. The re-optimizing method includes the steps that the first communication cost of the reconstructed unmanned-aerial-vehicle formation communication topology is calculated; the first communication cost is compared with the target communication cost of the minimum arborescence of a formation communication diagram in the preset state; when the first communication cost is larger than the target communication cost, the reconstructed unmanned-aerial-vehicle formation communication topology is optimized through the preset strategy. According to the re-optimizing method and system, the first communication cost of the reconstructed unmanned-aerial-vehicle formation communication topology is compared with the target communication cost, when the first communication cost is larger than the target communication cost, the reconstructed unmanned-aerial-vehicle formation communication topology is optimized through the preset strategy, and when the communication failure of the unmanned aerial vehicle in the formation appears, the communication cost of the re-optimized unmanned-aerial-vehicle formation communication topology is minimum.