HEVC achieves a better coding efficiency relative to prior standards, but also involves dramatically increased complexity. The complexity increase for intra prediction is especially intensive due to a highly flexible quad-tree coding structure and a large number of prediction modes. The encoder employs rate-distortion optimization (RDO) to select the optimal coding mode. And RDO takes a great portion of intra encoding complexity.Moreover HEVC has stronger dependency on RDO than H.264/AVC. To reduce the computational complexity and to implement a real-time system,this paper presents two low-complexity RDO algorithms for HEVC intra prediction. The structure of RDO is simplified by the proposed rate and distortion estimators, and some hardware-unfriendly modules are facilitated. Compared with the original RDO procedure, the two proposed algorithms reduce RDO time by 46% and 64% respectively with acceptable coding efficiency loss.