The mixing of the three primary colours of light is an interesting experimental phenomenon in second year physics, but in reality, students do not get satisfactory results when taught by various factors. In response to the shortcomings and defects of the original primary colour demonstrator, we have designed and built our own demonstrator for the mixing of the three primary colours of light after screening materials, modifying the structure and making several improvements. The demonstrator uses a diode as the light source, which provides stronger light and a larger viewing window. The intensity of each colour of light can be adjusted by using a potentiometer, and through innovative structural design, the mixture of different colours of light can be fully, equally or unequally proportioned.The demonstrator has been used to good effect in teaching