Background <p>Tibetan sheep represent valuable genetic resources on the Tibetan Plateau, and their body size and carcass traits serve as crucial foundations for breeding program development and breeding effects evaluation. The study of body size and carcass characteristics of Tibetan sheep helps to understand their process of genetic regulation.</p> Result <p>The body size traits, carcass traits, and muscle fiber structure of plateau-type Tibetan and Zhashijia sheep were compared. Zhashijia ewes displayed considerably higher carcass weight and body size than plateau-type ewes. Additionally, it was observed that Zhashijia rams exhibited significantly greater eye muscle area, chest width, and muscle fiber perimeter in comparison to plateau-type rams. And Glycogen staining results showed that the glycogen content of the plateau-type Tibetan sheep was significantly higher than that of the Zhashijia sheep. Through transcriptomic and proteomic analyses, we identified 366 genes that showed differential expression in the ram group and 248 proteins with differential expression. In the ewe group, we found 623 differentially expressed genes (DEGs) and 624 differentially expressed proteins (DEPs). Among these, eleven genes and fourteen proteins were associated with body size and carcass quality. These genes and proteins showed significant enrichment in the PPAR signaling pathway and protein digestion and absorption. Furthermore, employing weighted gene co-expression network analysis (WGCNA) allowed us to identify twelve genes that are pivotal in regulating body size and carcass. Finally, RT-qPCR validation confirmed the reliability of our RNA-Seq results.</p> Conclusion <p>The findings of this study contribute to a deeper comprehension of the morphological characteristics and carcass traits of Tibetan sheep, thereby establishing a robust scientific basis for the selective breeding of novel sheep breeds with enhanced growth performance and superior meat production capacity.</p>