Facing the higher demands for communication and sensing in upcoming Dual-Function Radar Communication （DFRC） systems， a DFRC system model was proposed that combines multi-cluster Non-Orthogonal Multiple Access （NOMA） technology and Reconfigurable Intelligent Surface （RIS）. In the proposed model， the superimposed multi-cluster NOMA signals were utilized by the DFRC base stations to achieve target perception and the virtual line-of-sight links established by RIS reflection were used to enhance the communication performance of users in multi-cluster NOMA. Based on the proposed model， with the goal of maximizing weighted sum of the system sum rate and the sensing power， a non-convex objective function with multiple constraints and coupled variables was constructed. To solve this objective function， an optimization scheme for joint beamforming and power allocation was proposed. In the proposed scheme， firstly， the original optimization problem was decomposed into three subproblems. Subsequently， methods such as Successive Convex Approximation （SCA） and SemiDefinite Relaxation （SDR） were employed to transform the original non-convex optimization subproblems into convex optimization subproblems. Finally， the Alternating Optimization （AO） method was applied to solve the subproblems， thereby achieving joint beamforming （including active and passive beamforming） and intra-cluster power allocation coefficient optimization. Simulation results indicate that the proposed scheme has good performance of communication and sensing， and compared with the Orthogonal Multiple Access （OMA） scheme， it has the system sum rate improved by about 1 bit/（s·Hz） with high target perception performance， achieving a good compromise between communication performance and perception performance.