A method for producing L-lactic acid is disclosed, which comprises the following steps: (a) culturing spores of Rhizopus oryzae in a medium containing a carbon source and a nitrogen source, forming dispersed mycelia, (b) seeding said mycelia into a fermentation medium containing ammonia; (c) starting the fermentation, meanwhile, the pH value is controlled in a range of 4-5 and the concentration of ammonia is in a range of 0.05-5 g/L; and (d) extracting the L-lactic acid form the fermentation medium, wherein the Rhizopus oryzae is Rhizopus oryzae ATCC 9363.