A red, green, and blue (RGB) tri-color visible light multiplexer/demultiplexer with excellent performances is the core component in optical display systems or visible light communication systems, undertaking an important task of light path control. At present, the widely used RGB multiplexer/demultiplexer mainly includes two types, one is based on prisms, other is made by fibers. Both types are composed of discrete components, lacking of integration. To satisfy the needs of system miniaturization and integration, we propose a Bragg grating-based RGB waveguide multiplexer/demultiplexer, and systematically study the relationship between tis performances and grating characteristic parameters such as grooving depth,and period number. The results show that a SU-8 RGB multiplexer/demultiplexer has a compact structure with cross section of only a few hundred nanometers and a length of dozens of microns, and exhibits better transmittance and flexibility than a traditional silicon materials component. The optical properties of the RGB multiplexer/demultiplexer are mainly affected by its grooving depth and period number. With increase of the groove depth, the central wavelength of the reflection spectrum exhibits red shift first and blue shift later, the width of the reflection spectrum increases almost directly, and the peak value of the reflection spectrum tends to saturate gradually. However, with the increase of the period number, the width of the reflection spectrum does not change significantly, and the peak value of the emission spectrum tends to saturate gradually. Based on such characteristics, our design realizes the RGB multiplexing/demultiplexing, laying a solid foundation for the miniaturization, integration, and flexibility of RGB multiplexer/demultiplexer.