The design of a hollow-core terahertz photonic crystal fiber (PCF) based on poly methylmethacrylate (PMMA) is reported in this paper. THz wave propagates inside the core large hole and the surrouding four cladding layers with small holes can confine THz wave propagation. By simulation in software COMSOL, the leakage loss of the designed PCF is found to be lower than 0.1 dB/m at 0.6 THz which is low at terahertz band. Similar to the radiation theory of metallic waveguide, the PCF can also be used as antenna to radiate energy. Its radiation characteristics are simulated. The simulated input reflection coefficient is less than -25 dB and the directivity of the antenna is greater than 20 dB. The half power beam width is about 13 degrees.