Abstract: A new root maggot pest was investigated and described in Chuoerhe Farm in Zhalantun City of Inner Mongolia. This study aimed to clarify the classification status and damage characteristics of soybean seedling root maggots. Root maggots were collected and artificially reared indoors, species were identified by morphological methods, and the morphological characteristics of each insect stage were described. A multi-point survey of the symptoms and damage on the site was used to conducted with the method of a random five-point sampling. In soybean field, this pest bored the rhizomes of seedlings by larva and caused the appearance of wilt and death, resulting in the lack of seedlings and ridge breakage. The percentage of infected plants was 22% in the seriously damaged plots. This pest can be transferred into other plants in field. The species identified the root maggot as the root maggot was Delia platura（Meigen）. It is firstly found that this pest damaged cultivated soybean in China. In order to facilitate identification and control in the field, a classification key was compliled based on the morphological differences between this pest and other three kinds of root maggot pests reported in China that can harm soybean.