I am wondering is this means the ax3 is dying slowly?
I just bought it in May 2023, and tried netinstall, but it is not work to reduce the percentage of bad blocks.

Netinstall will not change anything about it.
As long as the number is not increasing spectacularly on a short period, don’t worry too much about it.
Flash devices always have some bad blocks.
Edit: changed title. It’s zero point 7 %. Not 7%.
Thanks so much bro
Like above poster answered, all Flash chips have some bad blocks from the factory, it is natural. The only thing you need to monitor, if the number is not increasing every day, only then you can start to worry.