Abstract: As the focus of current research on hollow core photonic bandgap fiber, reducing fiber loss is of great importance. In the view of fiber design, taking the 19 cell hollow core photonic bandgap fiber for example, the relationship between structure parameters and loss characteristic was investigated using the finite element method. Simulation results indicate that the confinement loss can be effectively reduced by adjusting the cladding parameters. With the increase of the layer of air holes, the air filling fraction and the fillet diameter at the corners, the confinement loss can be reduced below 10-4 dB/km. While the surface scattering loss, which depends on the coupling between the core mode and the surface mode, increases with the thickness of the core wall as well as the core expansion factor. In addition, the appearance of surface mode also leads to a sacrifice of transmission bandwidth. Limited by the fiber structure, the transmission loss of 19 cell hollow core photonic bandgap fiber is difficult to be reduced to less than 1 dB/km. Further reducing fiber loss can only be achieved by removing more air holes to form a larger hollow core structure. The research achievement provides theoretical basis for the realization of low loss hollow core photonic bandgap fibers.