The invention is concerned with the strains of B. coagulans for lactic acid production and the related methods, in which the carbon sources are pentose or hexose or the agricultural or industrial wastes containing pentose or hexose or a mixture of both. According to the invention, the highest amount of L-lactic acid produced from glucose is 173 g/L, the optical purity is over 99%, the yield is up to 0.98, and the productivity is up to 2.4 g/L per hour. The highest amount of L-lactic acid produced from xylose is 195 g/L, the optical purity is over 99%, the yield is up to 0.98, and the productivity is up to 2.7 g/L per hour. The highest amount of L-lactic acid produced from reducing sugars in xylitol byproducts is 106 g/L, the optical purity is over 99%, and the productivity is up to 2.08 g/L per hour. The B. coagulans strains XZL4 (DSM No. 23183) and XZL9 (DSM No. 23184) of the invention can directly utilize various reducing sugars in xylitol byproducts to produce high amounts of L-lactic acid, which improves the production efficiency at low costs, and the strains are, thus, appropriate for industrial productions.