An innovative ball-mill reactor was designed and made to produce dimer acid continuously. Mixing and polymerization in the constructed reactor were intensified by the rotation of the cylinder and mechanical actions of small beads. A total of 3 baffles were set up to enhance radial turbulence, and 10 clapboards were sequentially installed to separate the whole reactor into 11 small reactors in series in order to make it close to a plug-flow reactor. The relationship between reaction performance and the inner components (baffles and clapboards), ball-milling medium, rotating speed, wall temperature and residence time were investigated. The crude product containing 50.6% dimer acid was obtained under the optimal conditions (zirconia beads as ball-milling medium, wall temperature 300 degrees C, residence time 2.16 h, rotating speed 20 rpm). Ferric and nickel ion from the reactor and the uneven residence time distribution resulted in low dimer acid production yield.