With the advantage of being eco-friendly, plant dyes have been noticed by textile practitioners and the public. However, as a result of the rapid advancements in industrial manufacturing, the traditional knowledge of plant dyes is dying, which demands heightened attention and protection. To document this traditional knowledge in the Baiyi community, semi-structured interviews were conducted with 288 informants from four villages (Five stars village, Hedong village, Nanpo village, and Shang’ eping village) of the Liuhe Yi Nationality Township, Heqing County, Dali Prefecture. Based on the ethnobotanical investigation of plant dyes, there were 11 plant species from 11 genera in 10 families that have been used as dyes. The Baiyi Indigenous peoples mainly extract the dye from the roots, leaves, fruits, etc., of the herbaceous plants. Through quantitative analysis, the frequency of use (f value) and cultural importance indices (CI value) of Viburnum cylindricum are the highest. The optimal conditions for dyeing cotton fabric with V. cylindricum were found to be a pH of 5, dyeing for 30 min at 60 °C by an orthogonal array design. As for the dyeing properties, biomordants provided better properties when used in dyeing cotton fabric with V. cylindricum compared with metallic mordants. This study reveals the great potential of the application of plant dyes in the Baiyi Indigenous peoples community; it will be beneficial to the economic development of ethnic areas, the inheritance of ethnic culture and the protection of biodiversity.