Some facts which affect the emulsion contraction during the processing of holographic silver halide plate are analyzed. These facts such as the time of exposure,the temperature of bleaching as well as the dehydration method are studied experimentally. Based on the study,a method of controlling the emulsion contraction which determines the diffraction wavelength of the reflection holography is given and a multicolour holography is attained. The experiment result indicates that a good multicolour holography can be made.