The invention discloses a preparing method of a brake pad friction block. The preparing method comprises the steps that raw materials are subject to temperature rising in argon atmosphere to be in a molten state, and vacuum heat preservation is carried out, so that a first material is obtained; the first material is out of a furnace to be casted, the first material is cooled to 375 DEG C to 395 DEG C, and surface machining is carried out to obtain a second material; the second material is subject to temperature rising to reach Ta DEG C, austenitizing is carried out, heat preservation is carried out, the second material is taken out to be placed in a nitrate bath at he temperature of 200 DEG C to 220 DEG C, the material is subject to temperature rising to reach Tb DEG C, heat preservation is carried out, the material is subject to oil cooling to 100 DEG C to 120 DEG C, the material is subject to temperature rising to Tc DEG C to be tempered, heat preservation is carried out, and the second material is subject to air cooling to the room temperature to obtain the brake pad friction block; and Ta=1050+Ka*(nCo+nMo)/nNb, the value of Ka ranges from 60 to 70, Tb=355+Kb*(nCo+nMo)/nNb, the value of Kb ranges from 18 tp 20, Tc=200+Kc*100*(nNb+nCo+nMo), and the value of Kc ranges from 170 to 200.