A robot for testing performance of a spacesuit lower limb comprises a pressure-maintaining tank (7), an air circulation assembly, an air-cooling apparatus set (11), a flexible tubular heat dissipation assembly (9) and two mechanical legs. The air-cooling apparatus set (11) is connected to the pressure-maintaining tank (7). The air circulation assembly (11) is provided inside the pressure-maintaining tank (7). The mechanical legs are installed at the pressure-maintaining tank (7). The flexible tubular heat dissipation assembly (9) is provided inside the mechanical leg. After being cooled by the air-cooling apparatus set (11), air in the pressure-maintaining tank (7) is transferred to the flexible tubular heat dissipation assembly (9) by means of the air circulation assembly. The mechanical leg comprises an upper leg (1), a knee joint assembly (3), a lower leg (4), an ankle joint assembly (5), and a foot member (6). The upper leg (1) is connected to the lower leg (4) by means of the knee joint assembly (3). The lower leg (4) is connected to the foot member (6) by means of the ankle joint assembly (5). The knee joint assembly (3) is provided with a knee joint driving assembly (302) and a knee joint transmission assembly (303). The ankle joint assembly (5) is provided with an ankle joint driving assembly (502) and an ankle joint transmission assembly (503). The robot has high motion track control precision and an adjustable size, and is applicable to testing of lower limb performance of spacesuits having different sizes.