A gamma automatic adjusting method and a gamma automatic adjusting system are provided. The method includes steps as follows: acquiring parameters of main affecting factors a gamma value in a liquid crystal panel light alignment; using a gamma model upon detecting a varied parameter of the main affecting factor; calculating and outputting an adjusting parameter of the main affecting factor by the gamma model to a UV irradiating machine; and irradiating the liquid crystal panel by the UV irradiating machine according to the adjusting parameter to keep the gamma value within a predetermined range.