The capacitor placement problem for radial distribution network determines capacitor size and locations, so that the energy loss in the studied system is minimized. Optimal capacitor allocation is a Mixed Non Linear Programming problem, and is very challenging, especially for large system. In this paper, a decomposition algorithm is proposed, in which the capacitor allocation problem is divided into two sub-problem: determining optimal capacitor's size, which is formulated as a successive linear programming, and an elimination strategy to remove least effective capacitors. With this approach, the linear programming problem can be solved with very high performance LP solver such as CPLEX. The proposed algorithm has been validatedthrough test on real large distribution networks of Vietnam, with satisfactory result.