This paper presents an accurate indoor localization system based on sub-harmonic frequency modulated continuous wave (FMCW) radar where a 24 GHz frequency divider-by-10 is used as an active reflector tag. Indoor positioning measurements are performed using least-mean-squares (LMS) algorithm. Measurement results show that the system has a positioning accuracy of 26.8 cm and a positioning precision of 2.97 cm, which outperforms other state-of-the-art FMCW indoor localization systems. It also further proves the system ability to mitigate multi-path interferences in complex indoor environments.