In this paper, the instability of Q-switched laser pulse power output which was resulted from the phenomena of model target existed in Q-switched Nd-glass and YAG laser is reported. In order to dispel the phenomena of Q-switched laser waveform random modulation fundamentally, the pre-Q-switching and the Fabry-Perot (F-P) standard panel assemble were used, a steady Q-switched laser output in pulse width of 40 ns and pulse energy of 85 mJ was obtained. The stabilities of pulse energy and pulse power were ±2% and ±3%, respectively, line width was 6.9×10-4 nm, the probability of single longitudinal mode output was 89%. With above-mentioned method, the modulating phenomena of mode target was eliminated, the stable pulse power output of Q-switched Nd-glass laser was realized.