Abstract: Using a 20 W fiber coupled LD as the pump source, the experiment of the gain-swithed Nd3+:YVO4 microchip laser was presented. 1 Hz～25 kHz repetition rate controllable Q switched laser with several W was obtained. The gain-switching from rate equation was theoretically investigated, and through the numerical solution the laser characteristics are analyzed. When the pump current is higher than the current which generates the single pulse, increasing the pump current or increasing the width of the pump current will generate several sub-pulses in one pump pulse. The wider the pump pulse is, the more output sub-pulses will be included in pump pulse. Increasing the repetition rate, the output laser has the same repetition rate as the pump laser, but more sub-pulses will be output in one pump pu