The first pulse problem is very popular in high repetition rate Q-switched laser, which is negative in the industry application. And it also leads to unnecessary energy loss. The mechanism of the first pulse control is analyzed on the partly end pumped E/O q-switched slab laser based on laser rate equations. A model of laser pulse generating is set up, by which the first pulse can be controlled by applying modulated high voltage on Pockels cell. The results of theory and experiments are also given.