Novel multi-wavelength laser, based on semiconductor optical amplifier (SOA) and cascaded two-stage sampled fibre gratings, is theoretically and experimentally investigated in this paper. The reflection spectrum of the sampled fibre grating and lasing output spectrum are calculated. Exploiting SOA and sampled fibre grating manufactured by our laboratory,a multi-wavelength laser with 11 wavelengths, in which the output power difference is smaller than 1dB, is achieved. Compared with the scheme based on the ordinary sampled fibre grating, more lasing wavelengths and more uniform lasing output power can be achieved in the novel scheme, which can be concluded from both theoretical calculation and experimental analysis.