Abstract: Terahertz fiber is one of the essential components in the terahertz system. In order to realize minimum low loss and dispersion of terahertz transmittion, a novel hollow terahertz fiber was designed and optimizated, which was based on Topas COC. Using the commercial software COMSOL based on the full-vector finite element method, the transmitting characters of this hollow terahertz fiber were calculated and the effects of the structural parameters on transmitting THz wave in the porous fiber core were analyzed. The research shows that adopting designed porous structure can confine the mode energy in porous core, and obtain small mode area, low propagation loss and nearly zero ultra-flattened dispersion. Increasing rate of the hole diameter to the hole spacing, the more mode energy can be confined in the porous fiber core, and the effective mode area and effective mode loss were reduced, but the confine loss and dispersion would be enlarged simultaneously.