Abstract: An E-O Q-switched solid state Nd:YAG laser system including an oscillator and an amplifier is introduc ed.Intensive discussion and analysis are focused on an abnormal phenomenon:aleaked laser beam with quite high energy is reflected from one side of the polarizer.The leaked laser is detected,then a profound analysis is given to point toil lustrate the detected waveform.It has al so been discussed in detail how to improve the efficiency of the laser quality on some aspects.Finally,it is concluded how to make use of this phenomenon's wave form to guide the debugging of this kind of lasers.The conclusion has a great importance in industrial manufacture of the lasers.