In order to investigate the species and categorization of Gasterophilus in Ili horse.We analysised the COI gene of the identified Gasterophilus dominant species and constructed NJ phylogenetic tree in the study.The results showed that infection rate was 100％ in total of 16 775 the third phase Gasterophilus instar larvae.Four Gasterophilus species were identified,and showed serious mix infections.Dominant species were Gasterophilus nasalis,its relative dominance were 53.17％,and prefer to live in the cardia,others to irregular live in the pylorus of the horses.COI gene homology of GasterophiIus nasalis,Gasterophilus intestinalis,Gasterophilus pecorum,Gasterophilus haemorrhoidalis (GenBank Accession No.:GU265752.1,KR230402.1,KU578262.1,KT946620.1) were 99％,99％,99％ and 100％ respectively.Phylogenetic analysis results showed that the data were clustered with the Gasterophilus app.which publshed on the GenBank.G.intestinalis and G.haemorrhoidalis cluster together first,and then cluster with G.nasalis,at last all three kinds of Gasterophilus cluster with G.pecorum.When the COI gene is the target,in-group and out-group of the Gasterophilus can forms an independent evolutionary branch.This study provides useful parameters for the classification of Gasterophilus.