A wavelength selective switch and a wavelength selection method are provided, where the wavelength selective switch includes: a dual-microring resonator, including a first microring and a second microring that are connected in series, where the first microring and the second microring respectively include one annular PN junction, and a direction of the annular PN junction of the first microring is the same as that of the annular PN junction of the second microring; an electric tuning module, where a first electric port of the electric tuning module is connected to a P zone of the first microring and an N zone of the second microring, a second electric port of the electric tuning module is connected to an N zone of the first microring and a P zone of the second microring; and a thermal tuning module, configured to adjust an operating temperature of the dual-microring resonator.