A one-meter-long high nonlinear photonic crystal fiber is pumped by laser pulse train at room temperature, and the generated correlated idler and signal photons are centred at 830 nm and 1411 nm, respectively. The full widths at half maximum of the broad band filters of the two channel are 15 nm and 35 nm, respectively. The fitting results of single channel photon counts reveal that almost all the photons originate from spontaneous four wave mixing and the influence of Raman scattering is eliminated. When the production rate is 0.0085 photon per pulse, the ratio between coincidence rate and accidental coincidence rate is measured to be 102, which not only confirms the low noise property of the photon pair, but also shows that the photon pair are naturally narrow band, and the collecting efficiency in our experiment is high. Moreover, these high purity photon pairs connect different optical bands, and have potential applications in quantum information technologies.