NOVELTY - Method for producing L-alanine by mutating lactate-producing bacteria, involves culturing Lactobacillus delbrueckii subsp.bulgaricus, preparing bacterial membrane, performing ion implantation, eluting bacterial membrane, coating eluent on solid flat plate, selecting ion implanted single bacterial colony, performing anaerobic fermentation, filtering the bacteria, adding agar and inhibitor, coating indicator bacteria, obtaining two L-alanine high-yielding strains, fermenting strains, filtering culture, condensing filtered solution, and separating L-alanine.    USE - The method is useful for producing L-alanine (claimed).    ADVANTAGE - The method utilizes low energy ion implantation mutation that enables wide mutation spectrum, low mortality, high direct mutation rate and stable property and utilizes glucose as raw material which is renewable natural resource, has wide source and is cost-effective, reduces power consumption as anaerobic fermentation is performed, reduces production cost, ensures product quality, and is suitable for large scale industrial production.    DETAILED DESCRIPTION - Method for producing L-alanine by mutating lactate-producing bacteria, involves (a) culturing starting bacteria Lactobacillus delbrueckii subsp.bulgaricus in slant medium at 42 degrees C to logarithmic phase, preparing bacterial suspension using 0.85% saline, diluting the bacterial suspension till 1 ml bacterial suspension contains 107 bacteria, after strains are detected to be strong and free from competitors through microscopic examination, absorbing 0.1 ml bacterial suspension, uniformly coating the suspension on sterile blank culture dish and blowing to prepare bacterial membrane, (b) performing ion implantation for the bacterial cells after detecting that the cells are not overlapped, where the implanted ions are nitrogen ions, the dose is 1.5x 1014-5x 1015 ions/cm2 and the energy is 15-20 keV, performing pulse implantation, implanting for 5 seconds with interval of 15-40 seconds, eluting the bacterial membrane after being subjected to ion implantation by 1 ml sterile normal saline, coating 0.1 ml eluent on solid flat plate and culturing in incubator at 37 degrees C, (c) selecting the ion implanted single bacterial colony, inoculating the colony to relative number of fermentation culture medium, performing anaerobic fermentation at 37 degrees C for 48 hours, where the pH value of fermentation solution is 6.5-7.5, filtering the bacteria from the fermentation solution, steam sterilizing the filtrate at 121 degrees C for 20 minutes, adding 1.5% agar, sterilizing at 115 degrees C for 20 minutes, adding 0.01-0.05% inhibitor, inverting the plate, coating the indicator bacteria and culturing in incubator at 36-40 degrees C, selecting mutant strain relative to the growth of indicator in the plate and obtaining two L-alanine high-yielding strains with number Lds 0108 and Lds 1109 by a stability test, (d) respectively performing slant culture and seed tank culture for the strains Lds 0108 and Lds 1109, where the slant culture is performed for 24 hours and the seed tank culture is performed for 18 hours, (e) inoculating the amplified seed solution to fermentation culture medium, where the substrate glucose concentration is 6-12%, performing fermentation at 35-40 degrees C for 30-52 hours, where the pH value of the culture medium is 6.5-7.5, maintaining anaerobic environment and finishing fermentation after the concentration of residual sugar is 0.1%, (f) performing ultrafiltration using ceramic or organic tubular ultrafiltration membrane and performing nanofiltration, and (g) condensing and evaporating the nanofiltered solution in vacuum, separating out L-alanine by crystallization, and centrifuging and drying to obtain the finished product.