this port have 1200 client。but when client online have 1023，after 1023 client can not connet network。and i can’t change 1023 to more bigger。how can solve this？
It is very strange.
According to the general switching rules in this case frames should be flooded (similar to a broadcast frames). Or new entry replaces the oldest entry in the table; both processes are usually invisible to the user.
Blocking does not occur ever.
good point
There are new CRS switch improvements in RouterOS v6.32rc5 which allow to overcome 1023 MAC learning limit per port.
Here are command examples to unset it on CRS ether1 port, similarly they apply to other ports
/interface ethernet switch port unset ether1 learn-limit
or
/interface ethernet switch port set ether1 !learn-limit