Carbon is an important element affecting the habitability of the Earth. The carbon cycle between the Earth’s surface and its deep interior has a very important impact on global climate change. Nowadays, the Earth regulates the global carbon cycle mainly through subduction and volcanism. However, the process of carbon cycle in the early Earth is significantly different from that in 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 the causes of the great oxidation event (GOE). The Earth was 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 early Earth magma ocean process, the differentiation between the Earth"s core and mantle will lead to the enrichment of carbon in the Earth"s core and the loss of carbon in the mantle; the interaction between the magma ocean and the Earth"s early atmosphere can bring the carbon from the atmosphere into the mantle. When the proto-Earth collides with a planetary embryo that has high C / N and C / S ratios could give rise to the carbon inventory in 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 P-T trajectory of ancient subduction is hotter than the modern subduction zone by 100℃. The subducted altered oceanic crust and ocean floor sediments would undergo complete decarbonation and carbonate melting at shallow depth, and only a small amount of carbon can be brought into the deep mantle by carbonated peridotite. The resulting greenhouse effect can get around the faint young Sun paradox. The early carbon cycle 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 for the formation of the great oxidation event.