I am an international student. I'm intending to take GRE test and i'm doubting if GRE test is accepted in UK's Universities.If the require english test is ielts,can someone submit both ielts and GRE tests? what is also the advantage of the GRE test for postgraduate studies ?

GRE is both maths and english. Some departments in the UK actually ask for GRE test scores if your undergraduate degree is from outside the UK (when applying for Masters or PhD). If it's a competitive department I'd advise you to take the GRE as it could count especially if your undergrad is from outside the UK.