Reconfigurable refractive surface (RRS) is regarded as a prospective technology for optimizing signal paths and enhancing directional propagation in complex environments, while non-orthogonal multiple access (NOMA) serves as an empowering technology to meet the high spectrum efficiency and large capacity requirements of the next-generation cellular communications. This paper investigates the problem of maximizing the sum rate of the downlink NOMA system assisted by RRS deployed in the near field of the base station (BS). The sum rate is maximized by alternately optimizing the power distribution and the phase shift matrix of the RRS. The Lagrange dual decomposition method is used to optimize the power allocation and then a phase shift rotation in turn (PSRT) method is proposed to optimize the phase shifts of RRS. Simulation results show that the sum rate of RRS-assisted NOMA systems is higher than that of RRS-assisted orthogonal multiple access (OMA) systems, NOMA systems and OMA systems.