A wavelength selective switch WSS, wherein the WSS comprises: N input ports, wherein N is a natural number greater than 1; an input-side fiber array connected to the N input ports; an input-side collimator array connected to the input-side fiber array; an input-side beam deformation and polarization conversion component connected to the input-side collimator array; an input-side wave-demultiplexing component connected to the input-side beam deformation and polarization conversion component; an input-side switching engine connected to the input-side wave-demultiplexing component; a focusing transformation lens group connected to the input-side switching engine and comprising two identical aspheric convex lens that are placed in parallel, wherein a curvature from a center to an edge of a surface of the aspheric convex lens changes continuously, and is used to control focal lengths of light with different wavelengths; and a spatial position of the focusing transformation lens group and the curvature from the center to the edge of the surface of the aspheric convex lens are so set that light with different wavelengths from the input-side switching engine is focused to a corresponding position of an output-side switching engine respectively; the output-side switching engine connected to the focusing transformation lens group; an output-side wave-combining component connected to the output-side switching engine; an output-side beam deformation and polarization conversion component connected to the output-side wave-combining component; an output-side collimator array connected to the output-side beam deformation and polarization conversion component; an output-side fiber array connected to the output-side collimator array; and M output ports, wherein M is a natural number greater than 1. N input ports, wherein N is a natural number greater than 1; an input-side fiber array connected to the N input ports; an input-side collimator array connected to the input-side fiber array; an input-side beam deformation and polarization conversion component connected to the input-side collimator array; an input-side wave-demultiplexing component connected to the input-side beam deformation and polarization conversion component; an input-side switching engine connected to the input-side wave-demultiplexing component; a focusing transformation lens group connected to the input-side switching engine and comprising two identical aspheric convex lens that are placed in parallel, wherein a curvature from a center to an edge of a surface of the aspheric convex lens changes continuously, and is used to control focal lengths of light with different wavelengths; and a spatial position of the focusing transformation lens group and the curvature from the center to the edge of the surface of the aspheric convex lens are so set that light with different wavelengths from the input-side switching engine is focused to a corresponding position of an output-side switching engine respectively; the output-side switching engine connected to the focusing transformation lens group; an output-side wave-combining component connected to the output-side switching engine; an output-side beam deformation and polarization conversion component connected to the output-side wave-combining component; an output-side collimator array connected to the output-side beam deformation and polarization conversion component; an output-side fiber array connected to the output-side collimator array; and M output ports, wherein M is a natural number greater than 1.