Objectives The key techniques of planting Mulato Ⅱ Brachiaria grass under walnut forests were studied to ensure a stable feed supply for the local beef cattle industry. Methods Three treatments including monoculture of Mulato Ⅱ Brachiaria grass, a mixed culture of Dactylis glomerata, perennial ryegrass, and white clover, and a monoculture of giant king grass were set up in the same walnut orchard in Longling County, Baoshan City, Yunnan Province for comparative planting experiment, with four replicates for each treatment. The production adaptability and stress resistance were observed, the biological yield was measured, and the economic benefits were calculated. Results Mulato Ⅱ was the dominant population after 25 days of sowing. The fresh grass yield of Mulato Ⅱ in 2022 and 2023 was 47 848.9 and 73 870.25 kg/hm², respectively, 66.9% and 87.2% higher than that of the mixed culture. However, the giant king grass did not meet the yield standards for two consecutive years. The average annual economic benefit of Mulato Ⅱ Brachiaria grass in 2022 and 2023 was 4 790.39 yuan/hm², higher than that of the mixed culture. Conclusions Mulato Ⅱ Brachiaria grass has a fast growth rate, strong resistance to local grass invasion, high heat and high humidity tolerance, and is green all year round with almost no pests and diseases. It can be promoted and planted as a high-yield and high-quality forage under walnut forests in areas at an altitude of 700-1 700 meters.