In order to study the hot cracking sensitivity of high alloying refractory superalloy GH4975, the crack morphology and microstructure characteristics of the ingot of GH4975 were observed, and the causes of hot cracking were analyzed by means of solidification behavior and thermodynamic calculation. The results show that the crack spreads along grain boundaries and dendrites, and the equiaxed crystal region has a greater tendency to crack than the columnar crystal region. Shrinkage holes are easy to appear in the center of the ingot. The formation of continuous shrinkage holes leads to insufficient overlap between dendrites, which is easy to be pulled apart under the action of stress to form a crack source. At the same time, the segregation of Al, Ti and Nb elements between dendrites is serious, and complex precipitates, especially a large number of (γ+γ ') eutectic phases, promote the nucleation and propagation of cracks. JMatPro's calculation shows that GH4975 alloy has a large shrinkage rate in the solid-liquid two-phase zone and a wide range of non-complementary temperature, which is easy to form a shrinkage hole and become a crack source. Meanwhile, the linear expansion coefficient of the alloy changes greatly in the non-complementary temperature range, and the crack is easy to expand.