Wavelength tunable optical ultrashort pulse generation by the use of a gain-switched Fabry-Pérot laser diode in a self-seeding simple scheme is presented. The laser external cavity consists of two fiber Bragg gratings (FBG) connected in series, an erbium-doped fiber amplifier (EDFA), an optical coupler and two circulators, which provides a mode selective and intensity controllable feedback to the laser diode. The system is simple and efficient, and sidemode suppression ratio (SMSR) of the output pulses obtained is close to or larger than 40 dB within a relatively wide wavelength-tuning range of 24 nm. The whole operating wavelength region is about 28.2 nm, between 1521.8 nm and 1550.0 nm, the SMSR obtained is better than 35 dB. The full width at half maximum (FWHM) of the pulse width is about 140～260 ps, and the FWHM of spectrum at different wavelength for any pulses is about 0.1 nm.