With D-optimum saturation design, a field experiment was conducted to study effect of nitrogen (N) application levels and transplanting periods on contents of reducing sugar and nicotine in flue-cured tobacco leaves. Results showed that the reducing sugar content decreased and the nicotine content increased with the increasing N rate, while the reducing sugar content increased and the nicotine content decreased with later transplanting. So it may be effective to enhance reducing sugar content and decrease nicotine content in tobacco leaves by rationally decreasing N rate and postpone transplanting date in Nanxiong.