Objective To clarify the species of stem nematode from diseased sample of Codonopsis pilosula in Gansu Province. Method Species identification of stem nematode was carried out by combing morphological analysis, phylogenetic analyses of ITS-rDNA and 28S-rDNA sequences, PCR with species-specific primers as well as PCR-ITS-RFLP.Result The morphological characteristics of the stem nematode population from C. pilosula in Gansu was similar to those of Ditylenchus arachis. The ranges of measurement values were basically agreed with those of D. arachis although some average values were different. The phylogenetic analyses revealed that the tested population was clustered into the same branch with D. arachis. The fragment amplified with specific primers, and PCR-ITS-RFLP map of this population were consistent with those of D. arachi. Conclusion The stem nematode population from C. pilosula in Gansu was identified as D. arachis based on morphological and molecular characters. D. arachis has occurred and distributed in Gansu.