In recent years, with the development of micro broadband white light sources, micro white light devices have exhibited great potential application value in many fields. As the core component of broadband white light technology, the compact, efficient and flexible RGB coupler plays a vital role. However, the traditional RGB coupler is composed of discrete components. Realizing miniaturization, flexibility and high transmission efficiency of the device is difficult, which greatly limits the development of micro white light broadband devices. In this paper, we propose an RGB on-chip waveguide coupler that can meet the requirements of miniaturization, flexibility, and high transmission efficiency and study its performance. The research results show that the device size is reduced to 0.04 mm×3.6 mm, and the average transmission efficiency in RGB beam multiplexing/demultiplexing is as high as 94.6%. In addition, the use of the SU8 polymer as a waveguide material makes our design compatible with flexible optoelectronic technology, which will greatly promote the development of miniaturization and flexibility for micro white light devices in the future.