Development of advanced light sources has become more and more important in the frontier scientific research. The development of new advanced light sources has pushed experimental studies from macroscopic world into the atomic and molecular levels, from studies of physical systems at static conditions to ultrafast dynamical processes, and from investigations at simple experimental conditions to more complex and real environment. Free electron laser (FEL) with high brightness, ultrafast laser pulses in the extreme ultraviolet (EUV) wavelength region is an ideal light source for excitation of valence electrons and ionization of molecular systems with very high efficiency. Dalian Coherent Light Source (DCLS) delivers 50-150 nm EUV beams with ultrafast pulse durations of 100 fs or ps to users. DCLS, as the first FEL user facility in China, has wide applications in the frontier researches of physics, chemistry, biology, especially in the field of basic energy sciences. This project is supported by National Natural Science Foundation of China and developed jointly by Dalian Institute of Chemical Physics and Shanghai Institute of Applied Physics, Chinese Academy of Sciences.