A new all-optical switching device, which is constructed by connecting an erbium-doped fiber with two symmetrical long-period fiber gratings (EDF-LPFG) pair was proposed. The transmission spectra of signal light for different pump powers in cross-phase modulation are simulated, and the transmissions of signal light as a function of the pump power under different effective index change and absorption coefficients are also discussed. The formula for threshold switching power of EDF-LPFG pair switch is derived. Compared with the single LPFG switch, the threshold switching power of EDF-LPFG pair switch is dramatically reduced by 5 orders, less than 25 mW. Such kind all-optical switch is hopeful to be used in future all-optical communication.