The invention discloses a nano ganciclovir freeze-drying preparation for injection and a preparation method thereof. The nano ganciclovir freeze-drying preparation for injection comprises the following components in parts by weight: 100-400 parts of ganciclovir, 10-50 parts of dextran 40, 5-50 parts of solubilizer, 10-100 parts of nano carrier material and 10-80 parts of freeze-drying skeleton agent. The preparation method comprises the following steps of: sequentially adding dextran 40, solubilizer, ganciclovir, nano carrier material and freeze-drying skeleton agent into water for injection to be dissolved, filtering a solution step by step, and carrying out freeze-drying, thus a freeze-drying preparation is obtained. According to the preparation method, no activated carbon is introduced, thus a risk that damage is done to a human body when activated carbon particles are introduced into the preparation as the activated carbon is used is avoided; besides, pH of the nano ganciclovir freeze-drying preparation for injection is 6-8 and close to that of plasma, and local irritation produced to the human body owning to overhigh alkalinity is avoided.