We investigate the propagation characteristics of the narrowband Stokes/anti-Stokes photons in cold atomic vapor. The four-wave mixing process results from parametric amplification of the anti-Stokes photons. We find that the process of parametric amplification is very similar to the light pulse propagating through an anomalous dispersion gain medium. Finally, we obtain the general solutions of the Glauber biphoton correlation functions, which are in good agreement with the experiment results.