Do clear command do not work in cygwin..
cygwin isn't one big thing that gives you all possible programs the instant it's installed. It lets you install whatever you want.
'clear' is part of ncurses.
Read here (not saying you should not ask questions, but google is your friend, always search first. Took me less than a second to find the below) 
hi
cygwin is very slow in processing, is there any way to make it fast
That is far too vague a question to be useful. cygwin, and most software in general, doesn't have a "go faster" mode. Why would anyone ever turn it off?
cygwin is also many programs that do many things and can be used in potentially incorrect or inefficient ways that have nothing to do with it being "slow" or because it's cygwin. What, exactly, is "slow"? What, exactly, are you doing? If a shell script is running slowly, please post the contents for us to look at.