Q-switched technique is one of the most efficient methods to produce high-peak-power and narrow-duration pulses. An all-fiber Q-switched laser based on the modulation of coupling loss is proposed and the Q-switching principles and relative parameters are analyzed. Two fibers are used in the laser cavity. The neighbor terminals of these fibers are placed end-to-end, one of which is mounted on a piezoelectric actuator (PZT). When a changed voltage outputted from a driver is applied to the PZT, a corresponding displacement of the fiber is generated. The displacement can be a longitudinal separation, a lateral offset or an axial tilt, which can modulate the coupling loss between the two fibers and change the round-trip loss in the fiber laser cavity as a result. When the lateral-offset mode is applied, Q-switching pulses are obtained up to the repetition rate of 10 kHz by changing the coupling loss efficiently. This method is easy and low cost, and increase its stability by external control.