The invention relates to a coarse wavelength division multiplexer based on a silicon-based nano beam loop structure and application thereof. The coarse wavelength division multiplexer comprises a nano beam and a directional coupler. The two sides of the nano beam are connected with two waveguides of the directional coupler respectively. The nano beam is a straight waveguide with a plurality of small holes etched. According to the nano beam, a Fabry cavity is formed by two reflection mirrors; and the central wavelength and the free spectrual range of the coarse wavelength division multiplexer can be changed by changing the cavity length of the nano beam. Therefore, the bending loss can be avoided; the multiplexer dimension can be reduced; the large FSR can be realized; and thus the coarse wavelength division multiplexer can be improved.