This paper presents a hybrid porous-core flexible photonic crystal fiber (PCF), which has the potential for low-loss guidance of broadband terahertz (THz) waves at low THz bands. Here, the cyclic olefin polymer TOPAS is used for the main material to increase the flexibility of PCF. The central hybrid porous-core area contains a circular and hexagonal design, which reduces the loss of PCF. Simulation results show that the proposed fiber has a very low confinement loss of 3.47 × 10 ^{− 6} dB / cm at 500 GHz operating frequency. The bending loss at a bending radius of 1 cm is as low as 3.2 × 10 ^{− 4} dB / cm. The negligible modal loss facilitates the flexible application to THz systems. Moreover, the fabrication of the proposed PCF design is compatible with widely used methods and technologies, including stacking and drawing, extrusion and drilling. This newly proposed hybrid design of the porous-core region can be considered as an improved version in the research of THz porous-core waveguides.