The co-flow jet (CFJ) is a new concept flow control method based on blowing and suction technology. Since it was proposed, it has gradually attracted extensive attention. This paper reviews the basic principles, concepts, research methods and progress of CFJ. The development of the CFJ concept is retrospected. The basic principle, wind tunnel experiment and numerical simulation are introduced. The application research on airfoils/wings, control surfaces, rotating blades and conceptual aircraft design are presented. Finally, several critical problems in the research of the CFJ are proposed, which could guide further research.