The invention discloses a method and a device for acquiring wavelength available for an OTU single plate. The method comprises the following steps: acquiring the current available wavelength set of a system and wavelength resource state information of all other OTU single plates, wherein all the other OTU single plates and the current OTU single plate are connected with the same wave combining and splitting type single plate; judging whether the intersection set of the currently used wavelength of all the other OTU single plates and the available wavelength set is empty, if the intersection set is not empty, tuning and evading the OTU single plate of which the current available wavelength is contained in the available wavelength set in all the other OTU single plates according to all the wavelengths supported by the intersection set, and eliminating the currently used wavelength of the OTU single plate which cannot be tuned and evaded from the available wavelength set; and acquiring the available wavelength of the current OTU single plate from the available wavelength set without the currently used wavelength of the OTU single plate which cannot be tuned and evaded. Through the method and the device, the mutual interference of optical signals can be avoided, and the reliability of the system can be improved.