Abstract: With the gradual increase of the penetration of renewable distributed generation（RDG） in the distribution network, the problem of insufficient RDG accommodation capacity for the distribution network has emerged in some areas. Objectively assessing the RDG accommodation capacity for the distribution network has become one of the important issues in the current distribution system planning and operation. Firstly, this paper demonstrates the mapping relationship of the impact of the uncertainty fluctuation of the injected power at any node in the distribution network on the operation state quantities such as node voltage distribution and branch currents. Secondly, this paper establishes the analytical expressions of the operation state quantities of the distribution network in different description forms such as random and affine for the uncertainty of the injected power of RDG.Then, the uncertain optimal power flow（OPF） model for RDG capacity assessment is proposed, and the deterministic equivalence transformation method of the OPF model in different description forms of RDG injection power uncertainty is established. Finally,the effectiveness of the proposed model and method is verified by an actual system.