Question

without oxyen how does sun burn?

Answer 1

sun burns  due to nuclear fusion of hydrogen(combining of hydrogen to form helium and so on ) which release a huge amount of energy in the form of heat and light .

Answer 2

In simple word, sun does not burn. We think its burning but its not, its an illusion. Nuclear fusion, where uncountable hydrogen nucleus are merged under great pressure, which looks like its burning. That's why it doesn't need oxygen. This is the perocess  we have in Hydrogen bombs.