Abstract: The couple equations with plan wave have been improved to describe focused Gaussian beam under big signal.With the improved equations,the SHG character of LBO has been analyzed under the condition of broad emission spectra of Yb-doped fiber laser.Main results are summarized as follows:in the case of all the emission spectra of Yb-doped,none critical phase match(NCPM) can be reached by temperature tuning.With increasing of wave length of fundamental beam,the SHG efficiency decreases a little,the acceptable temperature and the acceptable wavelength increase greatly,the acceptable angle increases not so obviously.It shows that an ideal SHG result can bring about using none critical phase match and long fundamental wavelength.