A low-loss coupling between photonic crystal fibers and standard single-mode fibers based on air holes filling is proposed.The impacts of filling parameters on coupling loss between the two kinds of fibers is investigated by numerical simulations via beam propagation method.The results show that this method can greatly reduce the coupling loss between two kinds of fibers provided the filling parameters are selected appropriately.This method is usable for the coupling between a variety of photonic crystal fibers and single mode fibers especially for those with large mismatch of mode field diameters.