Currently, the continuous rotary north-finder is widely discussed for its outstanding performance. However, few researches about the influence of turntable error on the continuous rotary north-finding algorithm can be found. For the north-finder based on rate biased RLG (ring laser gyro), the influence of turntable's periodic angular position errors to the north-finding results was studied. Theoretical analysis shows that, the existence of periodic angular position errors may cause unexpected error in the north-finding process and these errors must be modeled and compensated for in order to increase the north-finding precision. Finally, simulation and experiments were carried out to verify the theoretical conclusion.