Abstract: Let $T$ be a torus. On a manifold with a $T$-action which has finitely many fixed points, the integration of an equivariantly closed form can be evaluated as a finite sum of its moment map on the fixed point set. We will give a proof of this localization formula for circle action (assuming certain facts about finite-dimensional representations of circle). We will then work out an explicit example of integrating volume form of the 2-sphere using this formula.