A mutual pulse injection-seeding scheme is developed to generate tunable dual-wavelength optical short pulses by the use of two gain-switched Fabry-Pérot (F-P) semiconductor lasers. Multimode optical short output pulse is first generated by gain switching two F-P lasers with the approximate setup; Then by using two fiber Bragg gratings (FBGs) as filters, mutual injection locking of two wavelength optical pulses between two F-P lasers is realized by tuning optical delay line (VODL2), and dual-wavelength optical short pulse with high side mode suppression ratio is obtained at the output end. Wavelength selection and tuning are achieved by adjusting two FBGs and another optical delay line (VODL1), while a constant repetition frequency of 524.6 MHz is maintained. The side mode suppression ratio of the output pulses is better than 25 dB at a wavelength-tuning range of 13.2 nm. The system is stable and convenient for wavelength tuning.