I purchased electric braest pump....but its very painful...what's the reason..

which brand ? is the flange rubbing your nipple? if yes, that could be the reason for pain. remove the flange and try to use it

medfirst electric breast paump

is the suction power too high? can u adjust settings?

no in this suction power only on off ...no settings..

Every baby is different and their suction style and pressure is different. Also each mom is able to tolerate different suction. Hence a pump which allows you to adjust speed and suction as per your comfort is what is recommended. High speed high suction need not produce more milk.