We designed a novel and low switching-power all-optical fiber switch. The highly nonlinear photonic crystal fiber and the bi-directional pumped Er-doped fiber amplifier are inserted into the Sagnac loop mirror simultaneously. The switching is realized based on cross-phase modulation because the symmetry of the loop is broken. The theoretical analysis shows that the switching-power is inverse proportional to the product of the amplifier gain and the nonlinear coefficient of the photonic crystal fiber. In our experiment, 40 mW switching-power and 15.9 dB switching-extinction are obtained; furthermore, the transmission of signal light is a cosine function of the peak power of the control pulse. All the results of experiment well agree with the theory.