A path selecting method, comprising: computing an end-to-end path for a newly added service according to network topology and a wavelength constraint, and assigning a wavelength to the path; computing performance of each existing service and performance of the newly added service in a network according to physical impairment information collected in the network, wherein the physical impairment information comprises a gain reference spectrum of each optical amplifier in the network; and performing impairment check on performance of each service, and performing path selection for the newly added service according to a result of the impairment check; characterized in that the computing performance of each existing service and performance of the newly added service in a network according to physical impairment information collected in the network further comprises: according to one or more parameters of a device that a path corresponding to each existing service and the newly added service passes, an optical fiber type, a modulation type of each channel, optical power of each channel, and residual dispersion that are collected, computing an end-to-end optical signal-to-noise ratio penalty corresponding to each existing service and an end-to-end optical signal-to-noise ratio penalty corresponding to the newly added service, and using an end-to-end optical signal-to-noise ratio penalty corresponding to each service as a parameter for evaluating performance of each service. computing an end-to-end path for a newly added service according to network topology and a wavelength constraint, and assigning a wavelength to the path; computing performance of each existing service and performance of the newly added service in a network according to physical impairment information collected in the network, wherein the physical impairment information comprises a gain reference spectrum of each optical amplifier in the network; and performing impairment check on performance of each service, and performing path selection for the newly added service according to a result of the impairment check; characterized in that the computing performance of each existing service and performance of the newly added service in a network according to physical impairment information collected in the network further comprises: according to one or more parameters of a device that a path corresponding to each existing service and the newly added service passes, an optical fiber type, a modulation type of each channel, optical power of each channel, and residual dispersion that are collected, computing an end-to-end optical signal-to-noise ratio penalty corresponding to each existing service and an end-to-end optical signal-to-noise ratio penalty corresponding to the newly added service, and using an end-to-end optical signal-to-noise ratio penalty corresponding to each service as a parameter for evaluating performance of each service. according to one or more parameters of a device that a path corresponding to each existing service and the newly added service passes, an optical fiber type, a modulation type of each channel, optical power of each channel, and residual dispersion that are collected, computing an end-to-end optical signal-to-noise ratio penalty corresponding to each existing service and an end-to-end optical signal-to-noise ratio penalty corresponding to the newly added service, and using an end-to-end optical signal-to-noise ratio penalty corresponding to each service as a parameter for evaluating performance of each service.