We have numerically and experimentally studied an electro-optic Q-switched 1064 nm Nd:YVO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> laser with sub-nanosecond output. An effective numerical model is demonstrated, in which the intracavity photon density and the population inversion density are defined as variables of temporal and spatial. Guided by the numerical results, the maximum 1064 nm output pulse energy of 275 μJ has been achieved with a pulse duration of 1.16 ns at 10 kHz repetition rate, which corresponding to the peak power of 237 kW. With the maximum output energy, the beam quality factors M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of 1.26 and 1.24 in horizontal and vertical directions are obtained.