Abstract: In this paper, it is discussed by experimental method that the relationship of titanium alloy laser welding quality and the plasma optic signal. It is discovered that the plasma plume during titanium alloy laser welding is stronger than mild steel laser welding, and the plasma optic signal can reflect the stability of laser welding process and the change of weld quality. The amplitude of optic signal has a little fluctuation around a steady level when the good weld achieved, and changes obviously when the width or penetration of weld altered under the different welding conditions. If a gap or mismatch existed before welding, the average amplitude of signal decreases greatly, but the characteristics of two kinds of signals are different. The gap resulted in the trong fluctuedtion of the signal and its average amplitude was very low. As mismatch increased in a little range, the amplitude became lower and lower. The experiments indicate that the amplitude of plasma optic signal and fluctuation can be used as characteristic signal for real-time monitoring and control for titanium laser welding.