Colour hologram making is an important part of research hologram display technology. Nowadays it has great influece upon improving the hologram display. Although different ways of producing colour hologram exist ,to get the better quality of colour hologram,a new way is found to produce it by diffraction colour separation method. The red,green and blue information code of a colour transparent film can be recorded on a black-and-white film with a three-colour grating. Monochromatic laser is used to reproduce at the same time the distributions of the recorded three-color colour information, and to record them on a holographic film to make a colour holographic image. The remarkable advantage is that there is no need to make three holographic images with information covered with colour selection, that the diffraction efficiency is high,and that the reproduced image is of clear and bright colour.