This paper presents a new structure for 3×3 all-optical switching based on 3×3 MMI couplers. The proposed switch can work at both wavelengths of 1550 nm and 1310 nm. Two nonlinear directional couplers are used as phase shifters. Analytical expressions and BPM are used to design and optimize the whole device structure. Important parameters of the switch are calculated by using the BPM.