A polarization splitter based on resonant tunneling phenomenon in three-core photonic crystal fibers (PCFs) is presented. The supermodes in three-core PCFs will be resonant if their effective refractive indices satisfy some conditions. Choosing the appropriate parameters of PCFs, one polarization light will be close to the resonant condition and the other will be far away from the resonant condition. In the end of PCFs, the light power of the two polarizations can be confined in different cores. Full-vector finite element method (FEM) is applied to calculate the effective refractive indices in three-core PCFs. Full-vector beam propagation method (BPM) is employed to analyze the performance of the splitter. Numerical simulations demonstrate that it is possible to obtain a 1.039-mm-long polarization splitter for 1.55-μm light, and the extinction ratio can reach -36.98 dB. In this case, the bandwidth with the extinction ratio better than -11 dB is 24 nm.