A method for commissioning a wavelength division multiplexing optical network during capacity expansion, comprising: calculating, according to a preset rule, initial power at a first network element of a wavelength service to be added; adding one or more wavelength services at the first network element according to the initial power; detecting power of each newly-added wavelength service in transmission at a second network element; separately calculating target power of each newly-added wavelength service at the first network element according to a detected value at the second network element and the initial power at the first network element; calculating end-to-end performance of an existing wavelength service and end-to-end performance of each newly-added wavelength service when each newly-added wavelength service reaches its respective target power, wherein the end-to-end performance comprises at least one of an Optical Signal to Noise Ratio, optical signal to noise ratio, an OSNR margin, a bit error rate and a Q factor; and adjusting the power of each newly-added wavelength service when each newly-added wavelength service reaches its respective target power and the end-to-end performance of the existing wavelength service and the end-to-end performance of each newly-added wavelength service meet their respective lowest threshold requirements; wherein the adjusting the power of each newly-added wavelength service comprises: sequentially using the newly-added wavelength services as newly-added wavelength services currently to be commissioned and performing the following operations: calculating the end-to-end performance of the existing wavelength service when the newly-added wavelength services currently to be commissioned reach their target power; and adjusting power of the newly-added wavelength services currently to be commissioned to their target power when the newly-added wavelength services currently to be commissioned reach their target power and the end-to-end performance of the existing wavelength service meets its lowest threshold requirement. calculating, according to a preset rule, initial power at a first network element of a wavelength service to be added; adding one or more wavelength services at the first network element according to the initial power; detecting power of each newly-added wavelength service in transmission at a second network element; separately calculating target power of each newly-added wavelength service at the first network element according to a detected value at the second network element and the initial power at the first network element; calculating end-to-end performance of an existing wavelength service and end-to-end performance of each newly-added wavelength service when each newly-added wavelength service reaches its respective target power, wherein the end-to-end performance comprises at least one of an Optical Signal to Noise Ratio, optical signal to noise ratio, an OSNR margin, a bit error rate and a Q factor; and adjusting the power of each newly-added wavelength service when each newly-added wavelength service reaches its respective target power and the end-to-end performance of the existing wavelength service and the end-to-end performance of each newly-added wavelength service meet their respective lowest threshold requirements; wherein the adjusting the power of each newly-added wavelength service comprises: sequentially using the newly-added wavelength services as newly-added wavelength services currently to be commissioned and performing the following operations: calculating the end-to-end performance of the existing wavelength service when the newly-added wavelength services currently to be commissioned reach their target power; and adjusting power of the newly-added wavelength services currently to be commissioned to their target power when the newly-added wavelength services currently to be commissioned reach their target power and the end-to-end performance of the existing wavelength service meets its lowest threshold requirement. sequentially using the newly-added wavelength services as newly-added wavelength services currently to be commissioned and performing the following operations: calculating the end-to-end performance of the existing wavelength service when the newly-added wavelength services currently to be commissioned reach their target power; and adjusting power of the newly-added wavelength services currently to be commissioned to their target power when the newly-added wavelength services currently to be commissioned reach their target power and the end-to-end performance of the existing wavelength service meets its lowest threshold requirement. calculating the end-to-end performance of the existing wavelength service when the newly-added wavelength services currently to be commissioned reach their target power; and adjusting power of the newly-added wavelength services currently to be commissioned to their target power when the newly-added wavelength services currently to be commissioned reach their target power and the end-to-end performance of the existing wavelength service meets its lowest threshold requirement.