Hi,
a public range of IP address is routed to Router A from Router B. Also the default gateway of Router A is Router B.
these IP used for PPPoE users. when a user is offline and I try to TRACE it' IP address, it will redirect to Router B and Router B redirect it to router A an so on.

Any way to fix it?

this looks like a Routing loop. Check Your Routing table. is the Networks pinting to eachoter?

Yes, this is a routing loop.

On router A (where your pppoe ac is?) you have to create a static route with destination your whole pppoe subnet and type unreachable.

Yes, this is a routing loop.

On router A (where your pppoe ac is?) you have to create a static route with destination your whole pppoe subnet and type unreachable.

Thanks
Fixed.