In order to ensure the healthy and sustainable development of cold-water fish culture industry, and to ensure consumers’ clear consumption and strengthen the market supervision, it is necessary to find an effective method for species identification of salmon and trout. In this study, cytochrome oxidase I gene (COⅠ) was used to develop a simple, economical and efficient molecular identification method, aiming at identifying O.mykiss. The results showed that COⅠ gene could distinguish diploid rainbow trout, Salmo salar, Oncorhynchus keta and Coregonus peled, but could not distinguish golden trout and triploid rainbow trout. In the follow-up study, we will try to identify related species according to other methods. In production practice, this method could provide a gene tag to identify O.mykiss, and provide technical support for its species identification and healthy development of industry.