The invention discloses a concrete mixer. The concrete mixer comprises a support, a mixing drum and motors. The concrete mixer further comprises wheels, supporting legs, a lifting device, a first belt pulley, a cavity, a belt, supporting columns, a second belt pulley, a fixed platform, mixing blades, a feeding opening, a first mixing shaft, a sealing cover, bearings, a discharging opening, grinding balls, a second mixing shaft and a rough plate. The supporting legs with the wheels are arranged on the lower portion of the support. The mixing drum is disposed on the support. The first mixing shaft with the mixing blades is arranged in the center of the mixing drum. The two ends, stretching out of the mixing drum, of the first mixing shaft are fixed to the supporting columns through the bearings respectively. One end of the first mixing shaft is inserted in the fixed platform. The second belt pulley is arranged at the end, stretching out of the fixed platform, of the first mixing shaft. The second belt pulley is connected with the first belt pulley through the belt, and the first belt pulley is arranged on the motor in the cavity. The second mixing shaft provided with the grinding balls and connected with the corresponding motor is further arranged on the lower portion of the mixing drum. The concrete mixer is high in mixing efficiency and capable of grinding large-grain concrete.