Starting from the rate equations of acoustic opticalmodulated cavity dump ing Nd∶YAG laser, the dynamical processes of the number of atoms excited to the upper laser level and the number of coherent photons in the cavity have been analyzed theoretically both in laser buildup period and dump ing period.Some key parameterswhich affect the dump ing efficiency aswell as the laser pulse length have been discussed in detail.At the same time, an acoustic-opticalmodulated cavity dump ing Nd: YAG laser continuously pumped by laser diode has been studied experimentally. High repetition rate laser pulses as high as 1. 2MHz has been achieved, the pulse width is about 120ns, and the average laser power is 9W.