In order to obtain high power 780nm laser with simple structure and relatively low cost, the method of out-of-cavity frequency doubling with single frequency doubling crystal was adopted. After continuous wavelength laser generated by distributed feedback semiconductor lasers was injected into the optical fiber amplifier, quasi-phase matching was performed through periodically polarized lithium niobate crystals. The saturated absorption spectra of rubidium were obtained. The results show that, 1.2W frequency doubling light is produced and the laser has high output power. This result is helpful for the miniaturization of cold atomic physics experiments such as rubidium atomic clock and atomic interferometer.