One critical issue related perovskite solar cells is their relatively low stability compared with other thin film solar cell technologies. In htis talk, I will present our progress in understanding the intrinsic stability of perovskite materials related to material structure and operation conditions, including strain, ferroelastic domain boundaries, light, and defects. Many of these properties are unique to halide perovskites in good and bad way in terms the impact to solar cell stability. And our pregress on stability enhancement will also be presented in ehnahcing the overall device stability under real device operation condition. It is shown that efficient perovskite devices (PCE>20%) can be made stable for over six months under one sun illumination at evevrated temperatures.