ln this paper, a double pendulum system is studied for analyzing the dynamic behaviour near a critical point characterized b9 non-semisimple 1:1 resonance. Based on normal from theory, it is shown that two phase-locked periodic solutions may bofircate from an initial equilibrium, one of them is unstable and the other may be stable for certain values of parameters. A secondary bifurcation from the stable periodic solution yields a family of quasi-periodic solutions lying on a two dimensional torus, further cascading bifurcnations from the quasi-periodic motions lead to two chaos via period-doublin9 route. It is shown that all the solutions and chaotic motions are obtained under positive dampin9.