After I marked the positions of all the implantation electrodes, the output format was not mat, but tsv and pos. I don't know how to import it into brainstorm?
When you export the contact positions, there are different formats that you can export to.
The BIDS .tsv are good options.
Then when importing the positions, be sure that you use the same File of Type option. See detailed instructions in here:
https://neuroimage.usc.edu/brainstorm/Tutorials/ECoG#Alternative:_Read_BIDS_electrodes.tsv