The Resources tab says that my RB450G has 40 bad blocks. It's brand new, I've just got it.
How does this affect me and what can I do?

re-install with netinstall

Anything under 100 is fine, but if you want to clear it, Netinstall will help

Anything under 100 is fine, but if you want to clear it, Netinstall will help

When i first bought 450G and updated into 4.8(through files menu),i've got 4 Bad Blocks,when i have did netinstall,the bad blocks still persist ,the router only for couple days,should i RMA to my distributor?

Mine's still 40 bad blocks and 41000 total sectors written.

As I said, 100 blocks is fine and will not affect how it operates.

Ok, that's good to know.

Afterall, I'm very happy with it, no bottlenecks at 100mbps bandwidth(CPU@30-50%).