An optically tunable optoelectronic oscillator(OEO) by tuning the wavelength without any electronic microwave filter is proposed and demonstrated to obtain continually tunable output frequency.The oscillating microwave is determined by the wavelength,the tunability of frequency is realized by a three-order dispersion-compensating fiber Bragg grating(FBG),and it is designed by the FBG reconstruction method.When the wavelength of input signal changes from 1 550.6 nm to 1 551.4 nm,the dis-persion will change from 340 ps/nm to 1 460 ps/nm,As a result,the output frequency changes from 6.5 GHz to 13.5 GHz,and the tunable range is large.