Abstract: The colour of irradiated diamonds is affected by irradiation source, irradiation dose, irradiation temperature, type of diamond, etc.Electron irradiation experiments were taken under the condition of beam energy 2 MeV, and beam intensity 10 mA for analyzing the spectral characteristics of diamonds after irradiation.When the irradiation dose reached to 10-12 MeV, the colour of diamonds began to alter.As the irradiation dose increasing, the hue and saturation of induced blue and green enhanced, while the brightness of diamonds reduced.The parts of natural Ⅰa type diamonds classified as G or higher and colourless CVD synthetic diamonds turned blue.The rate of irradiation dose did not impact the results obviously.Water cooling system controlled the temperature of specimen holder under 40℃, which kept the cracks of diamonds well.After irradiation, irradiated blue diamonds have higher transmittance in the range of 415-478 nm than the other colour diamonds.