Abstract: Kilowatt high power laser flexible transmission is a necessary link in the field of high power laser processing such as laser cleaning, laser welding, laser etching, and the low loss optical fiber with bend loss is the key device to realize high power laser transmission. At present, high power laser transmission fiber adopts large core diameter fiber, but there are some problems, such as large bending loss, poor flexibility and so on. Therefore, a large core diameter air clad micro structure optical fiber is proposed. The air holes in the fiber cladding can greatly reduce the risk of laser leakage, reduce the strict requirements of high temperature coating in the process of fiber preparation, and achieve kW laser output, thus offer the foundation for the flexible transmission of 10 kW high-power laser.