To satisfy the needs of system miniaturization and integration, a Bragg grating-based RGB waveguide multiplexer/de-multiplexer was proposed, and the relationship between its performance and grating characteristic parameters such as grooving depth and period number were systematically studied. The results show that a SU-8 RGB multiplexer/de-multiplexer 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/de-multiplexer 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, the proposed design realizes the RGB multiplexing/de-multiplexing, laying a solid foundation for the miniaturization, integration, and flexibility of RGB multiplexer/de-multiplexer.