The invention discloses a heat treatment method of a diamond composite material blank. The heat treatment method sequentially comprises the following steps that step 1, the assembled diamond compositematerial blank is placed into a vacuum hearth, and after heating is carried out to a first temperature under a vacuum condition, heat is preserved for a certain time; step 2, the blank obtained in the step 1 is continuously heated to a second temperature under the vacuum condition, heat is preserved for a certain time, and intermittent hydrogen charging and vacuumizing treatment are carried out on a vacuum furnace while the heat is preserved; and step 3, the blank obtained in the step 2 is cooled to a third temperature under the vacuum condition, filling of inert gas or nitrogen is carried out until normal pressure is reached, and the blank is continuously cooled to normal temperature. Compared with an existing purification vacuum treatment method, the oxygen content of the mixed powder in the diamond composite material blank is reduced less than 100 ppm from 600 ppm, the interface bonding strength of produced diamond composite material samples is improved by 5-10%, and the high cleanliness of the whole diamond composite material blank is realized.