The invention discloses a step-by-step inference method for business relationships of Internet autonomous domain systems, which comprises the following steps: firstly, based on a valley-free path principle, according to top-level autonomous domain system information and autonomous domain system degree information, carrying out principle inference on relationships between adjacent autonomous domain systems of each path in a path table; secondly, performing re-judgment on an autonomous domain system relationship with conflicts in principle inference by using a mode of combining probability inference and principle inference, preferentially determining a result with a high global inference proportion, and updating the principle inference according to a new result; and for the autonomous domain system relationship of which the inference result is still not determined, inference is carried out according to the autonomous domain system degree information, and finally the commercial relationship between the adjacent autonomous domain systems on the path in the routing table is obtained. According to the method, the accuracy of deducing the types of the business relations between the autonomous domain systems is effectively improved, and the method is suitable for Internet routing security and business relation analysis of the autonomous domain systems.