Advances in insertion device technology, top-up operation and superconducting RF cavities make it possible to generate high brightness X-ray with intermediate energy light sources, which leads a new trend in designing and constructing third generation light sources around the world. The development status and the remarkable technical features of intermediate energy light sources are reviewed, and the main SSRF properties are described in this paper. Advances in insertion device technology, top-up operation and superconducting RF cavities make it possible to generate high brightness X-ray with intermediate energy light sources, which leads a new trend in designing and constructing third generation light sources around the world. The development status and the remarkable technical features of intermediate energy light sources are reviewed, and the main SSRF properties are described in this paper.