We report the experimental generation of narrow-band paired photons through electromagnetically induced transparency and spontaneous four-wave mixing in a two-dimensional magneto-optical trap (2D MOT).By controlling the optical depth of the 2D MOT from 0 to 40,the temporal length of the generated narrow-band paired photons can be varied from 50 to 900ns.The ‘transition’ between damped Rabi oscillation and group delay is observed undisputedly.In the damped Rabi oscillation regime,a violation factor of the Cauchy-Schwartz inequality as large as 6642 is observed.In the group delay regime,sub-MHz linewidth (～ 0.65 MHz) paired photons are obtained with a generation rate of about 0.8 × 105 s-1.