The phase composition and microstructure of 27Cr44Ni5W3Al+MA ethylene cracking furnace tube were analyzed using XRD, OM, SEM and TEM. The results showed that the as-cast microstructures of the furnace tube were mainly composed of austenite matrix (γ phase) and fishbone multi-phase carbides on grain boundaries, the inside of the multi-phase carbides are lamellar M₇C₃, while the outside are blocky M₂₃C₆. In addition, two shapes of Ni₃Al (γ' phases) were observed, namely the granular distributed near the junction between M₂₃C₆ and γ, and the blocky adjacent to M₂₃C₆. Both of M₂₃C₆ and granular γ' are the cube-on-cube orientation relationships with the γ matrix ([101]γ∥[101]M₂₃C₆，(-111)γ∥(-111)M₂₃C₆，(11-1)γ∥(11-1)M₂₃C₆；[1-12]γ∥[1-12]M₂₃C₆，(-111)γ∥(-111)M₂₃C₆，(220)γ∥(220)M₂₃C₆。[101]γ∥[101]γ'，(-111)γ∥(-111)γ'，(11-1)γ∥(11-1)γ'；[1-12]γ∥[1-12]γ'，(-111)γ∥(-111)γ'，(220)γ∥(220)γ'). In addition, a large number of dislocations were observed in the as-cast microstructure, with sparse distribution away from M₂₃C₆ and dense distribution near M₂₃C₆. The precipitation mechanism of γ' and M₂₃C₆ during centrifugal casting was also discussed.