Subduction zones are important channels for surface and deep carbon exchange. The carbon content of primitive arc magma is relatively high (3000 ppm – 1.5 wt%), with over 2/3 coming from the recycling of subducted carbonates, but its Mg isotope composition does not show the expected carbonate contribution. Due to the difficulty in explaining the high carbon content of arc magmas through metamorphic decarbonization reactions, the dissolution of carbonates in sediments and altered oceanic crust by plate dehydration fluids is considered a key process in the carbon cycle of subduction zones. Research has shown that the carbon flux of arc magmas in cold subduction zones is significantly higher than that in hot subduction zones. The mechanism behind this is that in cold subduction zones, serpentine beneath the arc dehydrates and releases a large amount of fluid, which can dissolve and carry carbonates into the magma source zone; In the hot subduction zone, the pre arc dehydration is strong, and most of the carbon is released in advance, resulting in relatively limited fluid release from the sub arc plate and less carbon entering the magma source area. Given the similarity in the enrichment characteristics of fluid active elements between arc magma and pre arc serpentinite, when interpreting the geochemical characteristics of arc magma, it is necessary to consider the interaction between the fluid released by the subduction plate during the pre arc decarbonization process and the olivine rock at the bottom of the mantle wedge, and systematically study the effects of serpentinite petrification, carbonation, and plate fluid infiltration processes on the carbon magnesium cycle in the subduction zone.