@ gswang
1) Search for "acad.lin" file in you support paths. You can type (findfile "acad.lin") at the AutoCAD command line.
2) Navigate to the folder where "acad.lin" is found and open the file in Notepad.
3) Find the linetype you want to copy in the file, then copy (CTRL+C) the 2 lines in the text file.
4) Go to a blank line in the text file and Paste (CTRL+V) the copied lines.
5) After the "*" and the "," on the first line of text, change the name of the Linetype to what you want. NOTE: You can also adjust the look of the linetype in the rest of the text lines, but you will have to learn how to do it properly (search for "To Add a Simple Linetype to an LIN File" in AutoCAD Help).
6) Save the acad.lin file
7) in the drawing , you will have to LOAD the linetype; i.e. select the linetype for the layer, when the dialog comes up, select the "Load button", then find the new linetype name.
Here is a link for more info:
https://allaboutcad.com/tutorial-create-a-custom-simple-linetype/PS: You can also use the "Make Linetype" tool in Express Tools if you have them loaded (command MKLTYPE)