This utility model belongs to the field of concrete material durability testing technology, specifically relates to a long-term constant uniaxial compressive stress loading instrument for concrete. It consists of a loading screw, a spherical support, a pressure transmission plate, an upper seat of the pressure support, a lower base of the pressure support, connecting rods of the pressure support, and a sample being tested. There are two connecting rods of the pressure support, one end fixed to the upper seat of the pressure support, and the other end fixed to the lower base of the pressure support. The sample being tested is located between the two connecting rods of the pressure support. The two ends of the pressure transmission plate are provided with grooves, which respectively fit into the two connecting rods of the pressure support. A spherical crown-shaped groove is located at the center of the pressure transmission plate, and the spherical support is placed within the spherical crown-shaped groove of the pressure transmission plate. The loading screw is located at the center of the upper seat of the support, with the bottom of the loading screw connected to the spherical support.