_{The effect of carbon content on the solidification microstructure of single crystal superalloy DD90 was investigated. The results show that, with the increase of C composition, the value of primary dendrite arm spacing increases, and the range of solidification temperature expands. With the increase of C composition , the content of carbide increases, the carbide morphologies change from blocky shape to Chinese script-type, then link together to skeleton –like. With the increase of C composition, the number of γ/γ′ eutectic decreases, coarse primary γ′ phase decreases. With the increase of C composition, the solidification segregation of metal elements in solid phase generally deducts. C addition promoted the degree of segregation of Al, while reduced the degree of segregation of Re, Mo, W.}