Single-crystal superalloy is the key material of turbine blade and hot end parts in aerospace field. The second generation nickel-based single crystal superalloy has been widely used because of its low cost and excellent high temperature properties. At present, the research on microstructure of superalloys at high temperature mainly depends on SEM and TEM observation after heating and loading experiment. However, such kind of work lacks real-time characterization capabilities. Carrying out in situ experiments has an important significance for understanding the real time deformation behavior and microstructure evolution of superalloys. Therefore, the development of an in situ high temperature (above 1000 ℃) mechanical testing equipment for SEM faces huge challenges. In this work, high temperature tensile experiment at 1150 ℃ of a second generation single crystal nickel-based superalloy were carried out by means of a self-developed in situ heating tensile platform which can used in SEM. A high quality experimental data and serial SEM images were obtained in the course of tensile testing at 1150 ℃. The analysis of force-displacement curve shows that the yield strength and fracture strength of the specimen are 580 and 620 MPa, respectively. The sequential SEM images during this research confirm that there is no obvious shape and size change for γ and γ′ during the elastic deformation, and microstructure changing during plastic stage is mainly due to γ phase widening which is parallel to the stress axis. The results show that the original micro-voids of samples are the weakness in high temperature tensile test at 1150 ℃, the fracture direction is almost perpendicular to the stress axis, the crack propagated by passing the γ′ phase and through in the γ phase, and ultimately, temperature and stress induced adjacent holes connection leading to the sample fracture.