Abstract: Covalent Organic Frameworks (COFs) are crystalline organic porous materials connected by dynamic covalent bonds, which possess regular structure, low density, large specific surface area, adjustable pore size, strong monomer modifiability, and diverse functions. On the strength of these specific properties, COFs have attracted much attention in the research field such as gas adsorption and separation, catalysis, fluorescence sensing, optoelectronics and drug delivery. This review highlights the significant progress on COFs in recent years with emphasizing the design principle, synthesis strategy, crystal controlling, functionalization methods and application of COFs, and the future development trends of COFs are also put forward.