i have config the min frequency to 250, but when use conky to check, the min is 500.
Also when i kernel config show, the avoid frequency is show 125 and 250, is there any way to check it??

are you using load ideal by any chance?
it makes 500Mhz the lower limit
open xterm and run this, its best to copy/paste it

echo 125000 250000 > /sys/devices/system/cpu/cpu0/cpufreq/ondemand/avoid_frequencies

note: you can remove the 125000 if you want it to avoid 125Mhz but there's no point really.
and a quick tip
set the kernel up as you want it then run
kernel-config save matt1
you can change the last bit to what you want so you'll remember it, then its just a case of running
kernel-config load matt1
to load the settings

understood, thx