A method for establishing a wavelength connection with adjustable spectral bandwidth, comprising: receiving, by a first node on a network side, a first signaling message sent by a first node on a client side, wherein the first signaling message comprises a specified modulation format and required spectral bandwidth of a wavelength connection to be established, wherein the first node on the network side is a node on the network side adjacent to the first node on the client side; obtaining, by the first node on the network side through calculation according to the specified modulation format and required spectral bandwidth of the wavelength connection to be established, a network-side path of the wavelength connection to be established, and allocating a spectral resource according to the specified modulation format and required spectral bandwidth of the wavelength connection to be established; forwarding, by the first node on the network side, the first signaling message to a second node on the network side along the path, wherein the second node on the network side is a node on the network side adjacent to a second node on the client side, wherein the first signaling message carries the allocated spectral resource; forwarding, by the second node on the network side, the first signaling message to the second node on the client side, wherein the first signaling message carries the allocated spectral resource, so that the second node on the client side sets a modulation format and a spectral resource of the second node on the client side according to the specified modulation format of the wavelength connection to be established and the allocated spectral resource; receiving, by the first node on the network side, a second signaling message returned by the second node on the client side, wherein the second signaling message comprises the modulation format and the spectral resource that are set by the second node on the client side; and returning, by the first node on the network side, the second signaling message to the first node on the client side, so that the first node on the client side sets a modulation format and a spectral resource of the first node on the client side according to the modulation format and the spectral resource that are set by the second node on the client side, thereby completing establishment of the wavelength connection. receiving, by a first node on a network side, a first signaling message sent by a first node on a client side, wherein the first signaling message comprises a specified modulation format and required spectral bandwidth of a wavelength connection to be established, wherein the first node on the network side is a node on the network side adjacent to the first node on the client side; obtaining, by the first node on the network side through calculation according to the specified modulation format and required spectral bandwidth of the wavelength connection to be established, a network-side path of the wavelength connection to be established, and allocating a spectral resource according to the specified modulation format and required spectral bandwidth of the wavelength connection to be established; forwarding, by the first node on the network side, the first signaling message to a second node on the network side along the path, wherein the second node on the network side is a node on the network side adjacent to a second node on the client side, wherein the first signaling message carries the allocated spectral resource; forwarding, by the second node on the network side, the first signaling message to the second node on the client side, wherein the first signaling message carries the allocated spectral resource, so that the second node on the client side sets a modulation format and a spectral resource of the second node on the client side according to the specified modulation format of the wavelength connection to be established and the allocated spectral resource; receiving, by the first node on the network side, a second signaling message returned by the second node on the client side, wherein the second signaling message comprises the modulation format and the spectral resource that are set by the second node on the client side; and returning, by the first node on the network side, the second signaling message to the first node on the client side, so that the first node on the client side sets a modulation format and a spectral resource of the first node on the client side according to the modulation format and the spectral resource that are set by the second node on the client side, thereby completing establishment of the wavelength connection.