We demonstrate the generation of full C-band coherent and frequency-lock multi-carriers by using two recirculating frequency shifter (RFS) EDFA loops based on phase modulator with external injection-seeding. In our proposed novel scheme, only one phase modulator is used in each loop and two loops are used to generate long wavelength and short wavelength subcarriers, respectively. Full C-band with totally 178 subcarriers and 26 GHz subcarrier frequency spacing covering nearly 36.66 nm from 1527.54 to 1564.20 nm are obtained. The performance of 178 subcarriers with superior flatness less than 3dB and tone-to-noise ratio (TNR) larger than 20 dB after a wavelength selective switch (WSS) shows that this novel scheme is a potential technique for the future 10Tb/s optical communication.