A passive Q-switched Yb-doped photonics crystal fiber(PCF) laser is demonstrated using GaAs as the saturable absorber. The PCF core has a diameter of 21 μm and an numerical aperture(NA) of 0.04, resulting in transversal single mode wave guiding for 1020～1150 nm light, ensures the good beam quality of the laser. The laser is pumped by a high power laser diode .The pumped laser is coupled to the cladding of PCF through a self-regulating coupling system. A shortest pulse duration as 80 ns was obtained with the maximum repetition rate of 6.7 kHz, when the maximum average output power of PCF laser is 5.8 W.