To investigate the dependence of large gradual solar energetic particle (SEP) events on the associated flares, the correlation coefficients between the peak intensities of E>0 MeV, E>30 MeV and E>50 MeV protons and the fluence of associated solar soft X-ray (SXR) emission in the three longitudinal areas W0-W39, W40-W70 and W71- W90 have been calculated respectively. The derived correlation coefficients between the fluence of SXR emission and the peak intensities of E>10 MeV protons in the three longitudinal areas are 0.43, 0.58 and 0.39 respectively, while the correlation coefficients between the fluence of SXR emission and the peak intensities of E>30 MeV protons in the three longitudinal areas are 0.50, 0.80 and 0.37 respectively, and the correlation coefficients between fluence of SXR emission and the peak intensities of E>50 MeV protons in the three longitudinal areas are 0.54, 0.83 and 0.10 respectively. The correlation coefficients between CME speeds and the peak intensities of E>10 MeV, E>30 MeV and E>50 MeV protons in the well connected region are 0.56, 0.52 and 0.48 respectively. The statistical results suggest that E>10 MeV protons have a moderate correlation with associated flares, while both E>30 MeV and E>50 MeV protons have good correlation with associated flares. Higher energy protons have closer association with the associated flares, while lower energy protons have closer association with shocks driven by the associated CMEs.