Since the renewable energy penetration in electricity system is getting more and more increased, new strategy is desired to help accommodate the fluctuated renewable energy. This paper proposes a transient-state gas flow model based unit commitment of integrated electricity and gas system (IEGS) with a decomposition optimization scheme adopted to satisfy the privacy protection requirements of system operators. The problem is solved decomposedly in an iteration procedure and the convergence of solution is guaranteed as well. Case study is conducted on a 6-bus 7-node system to verify the effectiveness of renewable energy accommodation capability. Besides, comparison between centralized optimization and the proposed decomposed optimization demonstrates that the adopted decomposition optimization scheme can find the global optimal integer variables, which further verify the validity of the proposed strategy.