The cast microstructure of a new difficult-to-deform superalloy эк151, was observed by high resolution field emission scanning electron microscope. The effects of elements on the thermodynamic equilibrium phases were studied by Thermo-Calc software. The results show that there is serious segregation of Mo, Nb and Ti during the solidification, which promotes γ′+γ eutectic. The main precipitates of эк151 alloy are a large fraction of cubic γ′, some carbides, borides and μ phase. Higher Cr, Mo, Nb and Ti contents can improve the primary and final melting points. The contents of Al, Ti and Nb can influence the precipitation temperature and mass fraction of γ' phase. Contents of Cr and Mo promote precipitation of M23C6 and M6C respectively. Furthermore, the increment of Cr, Mo and W content leads to more precipitation of μ phase