The invention provides a preparation method of an Al5Ti1B intermediate alloy, comprising the following steps of: uniformly mixing the following components in percent by weight: 25 percent-30 percent of KBF4, 30 percent-60 percent of K2TiF6, 10 percent-30 percent of pure aluminum powder and 0 percent-10 percent of pure titanium powder; carrying out cold pressing on the uniformly mixed powder to bea precast block with the density of 50 percent-60 percent by a hydraulic machine and drying for 2 hours at 100 DEG C in a blast drying box; melting aluminum and raising the temperature to 800 DEG C-850 DEG C; pressing the dried precast block into aluminum melt by using a phosphorizer, wherein the weight ratio of the precast block accounts for 30 percent-45 percent; and standing for 20-40 minutes,stirring for 5-10 minutes, slagging-off and pouring and moulding. The invention can realize obviously controlling reaction velocity in the early period of the reaction, quickening the reaction progress in the middle period of the reaction, and reducing fluoride salt by-products in the later period of the reaction. The prepared intermediate alloy has the characteristics that the phase dimension ofthe Al3Ti is about 20 mu m, the dimensional homogeneity is good, the intermediate alloy are all in block shapes, and TiB2 particles are fine and are uniform in dispersion.