Carbon is an important element affecting the habitability of the Earth. The carbon cycle between the surface and the deep of the Earth has a very important impact on the global climate change. Nowadays, the Earth regulates the global carbon cycle mainly through subduction and volcanism. However, there are significant differences of carbon cycle between the early Earth and the present Earth. Based on the previous research results, this paper comprehensively discusses the source of the Earth’s original carbon, the process of the Earth’s early carbon cycle and its relationship with the great oxidation event. The Earth evolved from the solar nebula through the accretion of planetesimals. Part of the carbon on the Earth comes from the initial composition of the Earth, and part is obtained through giant impacts and late veneer. During the magma ocean period at the beginning of the Earth’s formation, the differentiation between the Earth’s core and mantle made the Earth’s core enriched carbon and the mantle extremely depleted carbon; the interaction between the magma ocean and the Earth’s early atmosphere can bring atmospheric carbon into the mantle. The collision between the proto-Earth and the planetary embryo with high C/N and C/S values can increase the carbon content of the Earth. In addition, the late veneer of chondrites enriched in volatiles can also bring additional carbon to the Earth. In the early stage of plate tectonics, the geothermal gradient of ancient subduction is about 100℃ higher than the modern subduction zone. The subducted altered ocean crust and ocean floor sediments will completely decarburize through decarburization reaction or melting at very shallow depth, and only a small amount of carbon can be brought into the deep mantle by carbonated peridotite. The resulting greenhouse effect can offset the impact of early solar luminosity deficiency on surface climate. The early carbon cycle process of the Earth is closely related to the great oxidation event. The increase of CO₂ content in the atmosphere, the burial of organic matter, and the difference of subduction efficiency between inorganic carbonate and organic carbon are the key factors to form the great oxidation event.