A method of fetching digital data and writing the digital data into a memory of a logic analyzer, which comprises the steps: designate at least a first region and a second region in a memory; set a first triggering condition and a second triggering condition; fetch digital data continuously and write it into the memory while analyzing; and then write first test data which have an identification to satisfy the first triggering condition into the first region, and write second test data which have an identification to satisfy the second triggering condition into the second region. And once the first test data or the second test data are found, stop writing the digital data into the corresponding regions.