A mathematic model of the laser diode array(LDA) side-pump composite crystal Nd:YAG/YAG disk laser is set up:LDA fast axis is upright to disk face and micro lens collimate the fast axis. Far-field divergence angle of the slow axis is calculated and simulated,the result shows:far-field divergence angle of the slow axis has approximately Gaussian distribution. Study shows that more diodes lead to better pumping intensity distribution; the least absorption coefficient of laser medium, the best pumping intensity distribution; the smaller distance between diode and laser medium, the worse pumping intensity distribution. The phenomenon can be observed from the experiment with different absorption coefficient of Nd:YAG/YAG ,the pumping intensity distribution becomes better when there is 0.6%