Abstract: Rainbow trout (Oncorhynchus mykiss) is an important cold-water fish with high nutritional and economic value in China, however, less researches of high-quality rainbow trout germplasm resources populations were reported. This study aimed to provide essential data for assessing the nutrient composition of rainbow trout muscle, trait screening and the breeding process of new species by comprehensively evaluating the muscle nutritional components and quality of representative breeding populations of rainbow trout in six different regions. The 2—3 years old rainbow trout originally from Mudanjiang, Heilongjiang (HM), Ningan, Heilongjiang (HN), Gansu (GL), Xinjiang (XY), Jilin (JB) and Liaoning (LB). Thirty fish from each population were divided equally into three replicates, and the composition and content of moisture, crude protein, crude fat, ash content, amino acids and fatty acids in muscle were measured according to the national standard. The results showed that there were significant differences (P<0.05) in moisture (66.50%—77.00%), ash (1.12%—1.43%), crude protein (19.00%—21.84%) and crude fat (2.04%—9.08%) among the breeding groups, and the crude protein content of HN (21.26%) and GL (21.84%) was significantly higher than the other populations (P<0.05). In addition, the protein content of arious groups was greater than 16.00% and met the Food and Agriculture Organization of the United Nations (FAO)/Word Health Organization (WHO) Standard (2013). Seventeen amino acids were detected in the six breeding populations with a total amino acid contents (TAA) were 15.27%—18.90%. The total amino acid components were significantly higher in LB and JB than those in the other four breeding populations (P<0.05), and also had higher essential amino acid index scores (EAAI). Among the 17 amino acids, Glu had the highest content (2.64%—2.88%), followed by Asp (1.58%—2.03%). The content of fresh amino acids was as high as 11.25%—11.79%, indicating that rainbow trout muscles were fresh and tender, and the amino acid index (AAS), chemical index (CS) and EAAI of all populations were higher than the standard of FAO. Twenty-three fatty acids were detected in the six breeding populations, containing eight saturated fatty acid (SFA), four monounsaturated fatty acids (MUFA) and eleven polyunsaturated fatty acids (PUFA), with contents of 17.81%—31.75%, 27.86%—30.35% and 40.25%—54.32%. The PUFA to SFA ratio was between 1.34 to 3.05. HN and XY had higher SFA than other populations, while HM and GL had higher PUFA than other populations. Additionally, JB and LB had relatively higher MUFA than other populations. Taken together, six representative breeding groups of rainbow trout have balanced muscular nutrients and meet the FAO/WHO standard, which provides germplasm resources for rainbow trout breeding.