This paper reports the research result of GaAg 2×2 asymmetric Mach-Zehnder waveguide switch/modulator. The mechanism of this device and the factors of crosstalk are analyzed. Instead of traditional Y-branches, two asymmetric X-junctions have used in the switch. An 3d B coupler with good performance is obtained. The device operating at λ=1.15 μm has a 12 V Switching voltage and a crosstalk ratio less than -22.4 dB. This kind of switch will find application in the switching arrays.