We demonstrate, for the first time to our knowledge, the strong recovery of the optical-optical slope efficiency of gamma-ray-irradiated Tm-doped fiber under 793 nm laser diode (LD) pumping. The fiber optical-optical slope efficiency, the fiber cladding absorption spectra, and the fluorescence spectra of the Tm-doped fiber before and after 500 Gy gamma-ray irradiation have been measured for comparison. It is found that the fiber optical-optical slope efficiency had significant degradation from 56.3% to 26.7% after irradiation and recovered to 40.8% after 15 h pump bleaching. Based on comparative analysis of fiber cladding absorption spectra among pristine fiber, irradiation, and bleaching, the reasons for the strong recovery have also been discussed.