Thanks for the help from Pro.Daniele and Dr. yuxiao. The problem has been solved.
Firstly,ensure the DEM is bigger than research area. The research area should be checked carefully. It must be smaller than the user defined DEM, or it will not be processed successfully follow-up.
Secondly, the problem is coordinates transformation.My first-time DEM is in UTM projection,and all parameters could be filled automatically in “DEM source selection”, so it looks OK . But in “DEM visualization” window, no X mark covering research area can be found.
Try to save the DEM in geographic coordinate instead of UTM and import the DEM again in the previous method. Then, the problem was solved. And in “DEM visualization ” window, the research area appears.