A wavelength selective switch, wherein: • at least one optical element is disposed in the wavelength selective switch, and the at least one optical element is successively arranged in the wavelength selective switch according to a sequence of processing optical signals; configured such that • a service optical signal transmitted by a service laser and a monitoring optical signal transmitted by a monitoring laser are separately input to the at least one optical element, and the wavelength of the service optical signal and the wavelength of the monitoring optical signal are different; • the at least one optical element is configured to: receive the service optical signal from the service laser, receive the monitoring optical signal from the monitoring laser, and perform same optical signal processing on the service optical signal and the monitoring optical signal according to a processing function of the at least one optical element, to obtain the service optical signal processed by the at least one optical element and the monitoring optical signal processed by the at least one optical element; and the service optical signal processed by the at least one optical element and the monitoring optical signal processed by the at least one optical element are output, wherein the monitoring optical signal processed by the at least one optical element is used for monitoring performance of the wavelength selective switch, • wherein the wavelength selective switch further comprises an optical detector and a monitoring module, the optical detector is connected to a last optical element of the at least one optical element, and the monitoring module is connected to the optical detector; • the optical detector is configured to perform optical power detection on the monitoring optical signal processed by the at least one optical element, to obtain an optical power detection value of the monitoring optical signal; and • the monitoring module is configured to: obtain the optical power detection value of the monitoring optical signal from the optical detector, obtain a flare central location of the monitoring optical signal according to the optical power detection value of the monitoring optical signal, compare the flare central location of the monitoring optical signal with a preset flare central initial location to determine a central frequency offset of the wavelength selective switch, and compensate for the central frequency offset of the wavelength selective switch. • at least one optical element is disposed in the wavelength selective switch, and the at least one optical element is successively arranged in the wavelength selective switch according to a sequence of processing optical signals; • a service optical signal transmitted by a service laser and a monitoring optical signal transmitted by a monitoring laser are separately input to the at least one optical element, and the wavelength of the service optical signal and the wavelength of the monitoring optical signal are different; • the at least one optical element is configured to: receive the service optical signal from the service laser, receive the monitoring optical signal from the monitoring laser, and perform same optical signal processing on the service optical signal and the monitoring optical signal according to a processing function of the at least one optical element, to obtain the service optical signal processed by the at least one optical element and the monitoring optical signal processed by the at least one optical element; and the service optical signal processed by the at least one optical element and the monitoring optical signal processed by the at least one optical element are output, wherein the monitoring optical signal processed by the at least one optical element is used for monitoring performance of the wavelength selective switch, • wherein the wavelength selective switch further comprises an optical detector and a monitoring module, the optical detector is connected to a last optical element of the at least one optical element, and the monitoring module is connected to the optical detector; • the optical detector is configured to perform optical power detection on the monitoring optical signal processed by the at least one optical element, to obtain an optical power detection value of the monitoring optical signal; and • the monitoring module is configured to: obtain the optical power detection value of the monitoring optical signal from the optical detector, obtain a flare central location of the monitoring optical signal according to the optical power detection value of the monitoring optical signal, compare the flare central location of the monitoring optical signal with a preset flare central initial location to determine a central frequency offset of the wavelength selective switch, and compensate for the central frequency offset of the wavelength selective switch.