Xylose-assimilating pathways were constructed in the parental Pediococcus acidilactici strain and evolutionarily adapted to yield a highly stable co-fermentation strain for L-lactic acid production. The phosphoketolase pathway (PK) was blocked for reduction of acetic acid generation by disrupting phosphoketolase (pkt) gene. The pentose phosphate pathway (PPP) was reconstructed for xylose assimilation by integrating four heterologous genes encoding transketolase (tkt), transaldolase (tal), xylose isomerase (xylA) and xylulokinase (xylB) into the P. acidilactici chromosome. The xylose-assimilating ability of the constructed strain was significantly improved by long term adaptive evolution. The engineered strain was applied to the simultaneous saccharification and co-fermentation (SSCF) under high solids loading of wheat straw. The L-lactic acid titer, productivity and xylose conversion reached the record high at 130.8 +/- 1.6 g/L, 1.82 +/- 0.0 g/L/h, and 94.9 +/- 0.0%, respectively. This study provided an important strain and process prototype for production of high titer cellulosic L-lactic acid.