The invention discloses a soil restoration agent for restoring heavy metal polluted soil and a preparation method thereof. The soil restoration agent is prepared from turfy soil, brown coal, porous modified biocarbon, composite bacterium powder, and medical stone. The preparation method comprises following steps: (1) weighing all raw materials according to a formula; (2) adding brown coal and medical stone into a pulverizer, and grinding the brown coal and medical stone; (3) adding all raw materials into a high speed mixing machine, stirring, and evenly mixing; and (4) carrying out wet granulation to convert the mixture into granules, namely the soil restoration agent. The raw materials are easily available, the preparation technology is scientific, and the soil restoration agent can restore soil polluted by various heavy metals, is capable of improving the quality and structure of soil and increasing the nutrients of soil, and creates great social benefits, economic benefits, and environmental benefits.