A design for a novel broadband directional coupler (1×3) based on an asymmetric three-core photonic crystal fiber (PCF) is proposed. The asymmetry core in the fiber is introduced by the enlargement of air holes in three-core PCF. Numerical investigations demonstrate that the operating wavelengths of the novel broadband coupler range from 1530.9 to 1644.8 nm. The uniformity is less than 0.4 dB and polarization-dependent loss is less than 0.2 dB. In addition, the proposed coupler shows large tolerance to the fiber parameters. In particular, the coupler with at least ±4% derivation of the fiber length (20.9 mm) can ensure that the work bandwidth is not less than 80 nm.