A lossless bandwidth adjustment method is provided, includes: A downstream node of an ODUflex path receives a request message from an upstream node of the ODUflex path, where the request message is used for requesting lossless adjustment of a bandwidth of the ODUflex path; the downstream node searches according to the tunnel identifier to obtain bandwidth information before adjustment of the ODUflex path, compares the bandwidth information before adjustment with the bandwidth information after adjustment, determines the number of tributary slots that need to be adjusted for a link between the downstream node and an adjacent upstream node, and selects a tributary slot that needs to be adjusted; indicates, through a label, a tributary slot after adjustment of the adjacent upstream node or the selected tributary slot that needs to be adjusted, and sends a tributary slot adjustment command to a data plane.