L-threonine is an essential amino acid which is widely used in feed and pharmaceutical industries. We recently engineered Corynebacterium glutamicum R102 ($AHV^r$) for improved production of L-threonine. Inactivation of genes metX and dapA encoding dihydrodipicolinate synthase and homoserine O-acetyltransferase, respectively, was firstly conducted by homologous recombination, which differed from the common random mutagenesis method. Then operon gene hom-thrB (O) and export gene thrE (E) from R102 were over-expressed alone or together to obtain a series of recombinant strains. qPCR was employed to evaluate the transcript quantification of the target genes. In flask fermentation, the newly constructed strain $R102{Delta}metX{Delta}dapA$ (pEC-Box) was able to accumulate 3.35 g threonine/L compared with 1.80 g threonine/L of strain R102 ($AHV^r$).