A lossless bandwidth adjustment method for an Optical Transport Network, comprising: Receiving, by a downstream node of a bandwidth-variable optical channel data unit ODUflex path, a request message from an upstream node of the ODUflex path, wherein the request message carries a tunnel identifier, tunnel ID, of the ODUflex path, bandwidth information after adjustment and a new label switching path identifier, LSP ID, the request message is used for requesting lossless adjustment of a bandwidth of the ODUflex path, and the request message is sent by a first node of the ODUflex path along the ODUflex path downstream node by node to a last node; Saving, by the downstream node, control information of an LSP after adjustment, wherein the control information comprises the tunnel ID, the bandwidth information after adjustment and the new LSP ID; Seaching, by the downstream node, according to the tunnel identifier to obtain bandwidth information before adjustment of the ODUflex path, comparing the bandwidth information before adjustment with the bandwidth information after adjustment, determining the number of tributary slots that need to be adjusted for a link between the downstream node and an adjacent upstream node, and selecting a tributary slot that needs to be adjusted; and Indicating, by the downstream node and through a label, a tributary slot after adjustment of the adjacent upstream node or the selected tributary slot that needs to be adjusted, and sending a tributary slot adjustment command to a data plane, so that the data plane performs tributary slot adjustment and ODUflex bit rate adjustment according to the tributary slot adjustment command. Receiving, by a downstream node of a bandwidth-variable optical channel data unit ODUflex path, a request message from an upstream node of the ODUflex path, wherein the request message carries a tunnel identifier, tunnel ID, of the ODUflex path, bandwidth information after adjustment and a new label switching path identifier, LSP ID, the request message is used for requesting lossless adjustment of a bandwidth of the ODUflex path, and the request message is sent by a first node of the ODUflex path along the ODUflex path downstream node by node to a last node; Saving, by the downstream node, control information of an LSP after adjustment, wherein the control information comprises the tunnel ID, the bandwidth information after adjustment and the new LSP ID; Seaching, by the downstream node, according to the tunnel identifier to obtain bandwidth information before adjustment of the ODUflex path, comparing the bandwidth information before adjustment with the bandwidth information after adjustment, determining the number of tributary slots that need to be adjusted for a link between the downstream node and an adjacent upstream node, and selecting a tributary slot that needs to be adjusted; and Indicating, by the downstream node and through a label, a tributary slot after adjustment of the adjacent upstream node or the selected tributary slot that needs to be adjusted, and sending a tributary slot adjustment command to a data plane, so that the data plane performs tributary slot adjustment and ODUflex bit rate adjustment according to the tributary slot adjustment command.