The invention provides a wavelength protection method based on wavelength utilization rate in a single link, and related link nodes have optical wavelength conversion capacity. The method introduces the concept of wavelength utilization rate, and requires that a network can calculate the wavelength utilization rate of each wavelength in a transmission link in unit time quantum according to the situation of transmission service; the calculation results are stored in an array in a descending order. When an error occurs to the wavelength in the link, first idle wavelength is searched in the link,if the idle wavelength exists, then the idle wavelength is used for alternative transmission; if the idle wavelength does not exist, then the wavelength utilization rate of the wavelength with erroris extracted form the array stored with wavelength utilization rate, and the wavelength with the lowest wavelength utilization rate is searched in the array in reverse order for alternative transmission. Therefore, the maximum protection of the transmission wavelength with higher wavelength utilization rate is realized, the invention is suitable for protection of important transactions and high capacity transactions, and the precision of the protection based on the wavelengths is further improved.