By simultaneously using both an acoustic-optic (AO) modulator and a Cr4+:YAG saturable absorber in the cavity, for the first time, a diode-pumped doubly Q-switched Nd:GdVO4 laser has been realized. The pulse duration is obviously compressed in contrast to the actively acoustic-optic Q-switched laser. By considering the Gaussian transversal distribution of the intracavity photon density and the longitudinal distribution of the photon density along the cavity axis as well as the influence of turnoff time of the acoustic-optic (AO) Q-switch, we provide the coupled rate equations for a diode-pumped doubly Q-switched Nd:GdVO4 laser with both an acoustic-optic (AO) modulator and a Cr4+:YAG saturable absorber. These coupled rate equations are solved numerically, and the dependence of pulse width, pulse energy and peak power on the incident pump power at different pulse repetition rates is obtained. The numerical solutions of equations agree well with the experimental results.