Are the core vocabulary of IELTS and TEM8 the same?

Slightly different. The vocabulary of IELTS is similar to that of TEM-8, but there are of course many academic vocabulary besides daily vocabulary in IELTS academic examination, and these academic vocabulary generally come from Greek and Latin.

My review method is to read articles similar to IELTS reading articles in foreign authoritative magazines, and then understand and remember important words according to the context.