The invention provides a Kudzu powder capable of being dissolved in cold boiled water and the preparation method thereof. The Kudzu powder consists of, by weight percentage, 72 to 80% and white sugar 20 to 28%, or puffed Kudzu powder 98% and aspartame 2%, and has a granularity of 40 to 60 mesh, wherein the sweetness of the aspartame is 200 times that of the white sugar; and each component contains water with a weight percentage equal to or less than 7%. The preparation method comprises adjusting the weight percentage of water in common Kudzu powder prepared by conventional process to 13 to 15%; puffing by a double-screw extrusion expansion machine at a temperature of 120 to 130 DEG C, under a pressure of 0.98 to 1.18 MPa, and at a feeding speed of 17 rpm and a screw rotation speed of 50 rpm; pulverizing the puffed Kudzu powder to 40 to 60 mesh; adding the pulverized Kudzu into white sugar or aspartame with 40 to 60 mesh; and stirring, metering and packaging. The Kudzu powder prepared by the method is an instant powder suitable for convenient usage for tour, evection and leisure, and can be dissolved in cold pure water, cold boiled water, warm boiled water and boiled water.