The folding door is composed of door frames, door panels, transmission components, arm components, transmission rods, and orientation devices, etc. When opened, the folding door can fold and store the door panels on one side, maximizing the space savings. For places with limited space, such as small-sized balconies, the connection areas between kitchens and bathrooms, it can make the space open and transparent when needed, improving the space utilization efficiency. It is suitable for partition purposes in workshops, shopping malls, office buildings, exhibition halls, and home decoration, etc. It can effectively play the roles of temperature insulation, dust prevention, noise reduction and sound insulation, and shielding.