A service traffic allocation method and apparatus, where first leaf node repeatedly sends a probe packet through each physical link of multiple physical links of the first leaf node coupled to a backbone node, for each physical link, the first leaf node receives a returned response packet through the physical link, where each response packet is returned by a second leaf node after a probe packet that is sent through a physical link arrives at the second leaf node, for each path, the first leaf node calculates a transmission parameter of the path according to multiple response packets received on the path to obtain the transmission parameter of each path, and the first leaf node allocates to-be-transmitted service traffic to the physical links according to the transmission parameter of each path.