The effect of heat treatment on the microstructure and mechanical properties of a high boron Ni3Al based cast superalloy was investigated by means of SEM, tensile test and durability test. The results show that when the solution temperature increases from 1080 ℃ to 1150 ℃, the volume fraction of γ" phase in dendrite dry decreases gradually, the form changes from blocky to spherical, and small tertiary γ" phase is precipitated inside the γ channel. When the temperature rises from 1080 ℃ to 1120 ℃, the skeleton-like primary borides are partially dissolved, and the granular secondary borides are precipitated. The precipitation tendency of secondary borides increases with the increase of temperature, and the borides are completely dissolved when the temperature rises to 1150 ℃. After aging at 900 ℃×10 h, the alloy with solid solution at 1080 ℃ has the ultimate tensile strength of 900 MPa and the lasting life of 144.5 h, and the comprehensive mechanical properties are the best, so the best heat treatment process of the test alloy is 1080 ℃×4 h→ air cooling +900 ℃×10 h→ air cooling.