Theoretical calculations by perturbative QCD suffer from uncertainties by so-called Renormalons. For high precision analysis of physical quantities, one needs to separate and remove renormalons from perturbative QCD calculations. I first explain how renormalons arise and how the leading renormalon has been successfully removed from the observables of Heavy Quarkonium, together with their physical interpretations. Then we propose a new method to systematically remove renormalons, which we call "Dual Space Approach." By going to a "Dual Space" we can separate and remove multiple renormalons simultaneously.