Low-power 1×2 optical switching in a double coupler ring resonator (DCRR) made by a silicon nanoscale waveguide b ased on two photon absorption (TPA) is analyzed theoretically. The TPA originates from a femtosecond pump light at 400 nm, which enters the DCRR together with a CW signal light at 1.55 mm through the input port. TPA makes the silicon free-carrier concentration change, which is proportional to the change of reflective index. Our numerical simulation shows that when average pump power reaches 2 mW, it will induce the 10- 3 refractive-index change and the π-phase shift of signal light, after which 1×2 all-optical switching can be realized.