i have a low CGPA and have been trying to apply for masters but haven't had any luck.i've been rejected by universities because of my GPA.How can i cover up for it.

Where are you applying? Do you have an expected overall grade?
You cant not really cover up your grades, however if you are in the US, isn't there the opportunity to resubmit papers to improve your gpa?
In the UK, a good 2:1 or First is required at Undergraduate, to progress to Masters level but I am unsure if that is widely used criteria.

yeah i applied in university of manchester but they rejected me.BTW how much gpa does 2:1 make?what i really wanted to know was how i can make up for my GPA? Any suggestions

You can't convert GPAs to UK grades, the system is too different. A 2.1 is 60% or above in an undergrad degree; this will seem low to people in the US, but I guess you can think of it as a B.

What qualifications do you have?

Try to do some good projects or research related to your major. If you got the chance to work with experienced people, ask them for recommendations. Recommendations plays a good roles as far as I know in the admission judgement. Or, try to lower your university ranking standards. Manchester is still considered a good university in the CS. If you applied to other university you may get a chance.