A wavelength selective switch, comprising: a first demultiplexing/multiplexing component, configured to split a multi-wavelength optical signal into multiple single-wavelength optical signals in space, wherein the multi-wavelength optical signal is input from an input port of the wavelength selective switch; a spatial phase modulator, configured to separately change a transmission direction of each single-wavelength optical signal comprised in the multiple single-wavelength optical signals, wherein the spatial phase modulator is further configured to split a first single-wavelength optical signal in the multiple single-wavelength optical signals into a first light beam and a second light beam, wherein the first light beam is incident on an output port of the wavelength selective switch, and the second light beam is incident on a monitoring port of the wavelength selective switch, characterized in that the spatial phase modulator is further configured to separately split, in different time instants, each single-wavelength optical signal comprised in at least two single-wavelength optical signals in the multiple single-wavelength optical signals into two light beams, wherein one light beam in the two light beams of each single-wavelength optical signal comprised in the at least two single-wavelength optical signals is incident on a same monitoring port of the wavelength selective switch at a different time point; a photoelectric detector, disposed at the monitoring port and configured to receive the second light beam; and a performance monitoring component, configured to perform performance monitoring on the second light beam received by the photoelectric detector. a first demultiplexing/multiplexing component, configured to split a multi-wavelength optical signal into multiple single-wavelength optical signals in space, wherein the multi-wavelength optical signal is input from an input port of the wavelength selective switch; a spatial phase modulator, configured to separately change a transmission direction of each single-wavelength optical signal comprised in the multiple single-wavelength optical signals, wherein the spatial phase modulator is further configured to split a first single-wavelength optical signal in the multiple single-wavelength optical signals into a first light beam and a second light beam, wherein the first light beam is incident on an output port of the wavelength selective switch, and the second light beam is incident on a monitoring port of the wavelength selective switch, characterized in that the spatial phase modulator is further configured to separately split, in different time instants, each single-wavelength optical signal comprised in at least two single-wavelength optical signals in the multiple single-wavelength optical signals into two light beams, wherein one light beam in the two light beams of each single-wavelength optical signal comprised in the at least two single-wavelength optical signals is incident on a same monitoring port of the wavelength selective switch at a different time point; a photoelectric detector, disposed at the monitoring port and configured to receive the second light beam; and a performance monitoring component, configured to perform performance monitoring on the second light beam received by the photoelectric detector.