The dynamic microstructure evolution and fracture mechanism of Ni-based cast superalloy MAR-M247 are investigated during tensile test at room temperature, 400 °C and 760 °C by an in-situ SEM high temperature tensile stage. The in-situ tensile test results show that the yield strength and ultimate tensile strength decrease slightly, and the tensile plasticity increases slightly from room temperature to 760 °C. There is no slip band during in-situ tensile test at room temperature; and there is only a small amount of slip bands near the fracture surface at 400 °C and 760 °C. With the increase of tensile temperature, the fracture mechanism is not change, and all of them are ductile transgranular fracture. Microcracks mainly originate from the rupture of carbides which dispersed in the grains and on the grain boundaries.