A novel design of photonic crystal fiber (PCF) combiners is demonstrated. First, collapse three rings of air holes near to the fiber core using the post-processing techniques of PCFs, to enlarge the core. Then, taper it. Finally, splice the tapered multi-photonic crystal fibers into a multimode fiber for output. The axial losses of the directly tapered combiners and the expanded core-tapered combiners at different incident wavelengths are simulated and compared. The results show that the transmission losses of the expanded core-tapered combiners are far below those of the combiners without using the technology.