In high power excimer laser system, in order to achieve short pulse amplification and fine spot uniformity, angular multiplexing technique is adopted. So there are many laser beams and optical transmission links, which make the system complicated. In order to ensure the system working stably and efficiently, it needs to monitor and evaluate the status of all the links of system, which means online measurement of each amplification stage and multiple laser beams. Therefore, considering the character of the high power excimer laser system, a measure technique based on time-sequence method is proposed and principle experiments are carried on. Using this technique, online measurement of multiple beams using only one set of measuring elements can be achieved. The merit of this method is not only measurement efficiency can be promoted, but also the complication and cost is brought down, and the system errors caused by different elements are also avoided.