The invention discloses a single bud cleft grafting method of walnut seedlings. The method comprises the following steps that a 1-4-year-old stock which has a diameter of 1cm or more is selected, and sheared at the position 10cm over the ground; the middle part of the stock is vertically split for about 5cm by a knife; a pair of symmetric inclined planes are cut on two sides of the grafted scion, wherein the length of the inclined planes is 5-6cm, and the thickness at the lower end of the scion is about 0.2cm; then, the end, with the cut planes, of the grafted scion is quickly inserted into the cut of the stock, and the cambium of the scion and the cambium of the stock are aligned; and finally, a polyethylene film which is 3-4cm wide is used for fastening the grafted position from bottom to top in a manner of being loose firstly and tight afterward, so that the grafted scion is tightly enclosed. The method has the beneficial effect that the cleft grafted seedling is tightly connected and cannot be broken by wind after surviving, the grafted position is well healed, and the grafting survival rate is high.