The invention relates to the field of wireless communication, and discloses a transmitting method based on a sub-band and a device thereof. Under the condition that the CP length needs to be changed, by correspondingly expanding the lengths of DFT and IFFT and changing the partial length of transmission symbol data, the method and the device can keep transmission properties such as carrier recovery, timing recovery and the like except Doppler effect unchangeable at the same time of keeping the spectrum efficiency stable. A system can have one sub-band or a plurality of sub-bands. By distributing one data stream into the plurality of sub-bands to be transmitted, the method and the device have good power peak-to-average ratio and frequency domain selective interference resistance.