The invention relates to a mixer, in particular to a concrete mixer for buildings. According to the technical scheme, the concrete mixer for the buildings comprises a mixing drum, wherein a feeding device is arranged on one side of the mixing drum, a hydraulic oil tank is arranged at the upper part of the mixing drum, a hydraulic cylinder connected with the hydraulic oil tank is arranged at the upper part in the mixing drum, the lower end of the hydraulic cylinder is connected with a horizontal fixing plate capable of sliding up and down in the mixing drum, a rotatable rotating shaft is arranged on the lower end surface of the horizontal fixing plate, the rotating shaft is connected with a power output shaft of a motor on the horizontal fixing plate through a belt wheel on the rotating shaft, a cross rod perpendicular to the rotating shaft is connected to the lower end of the rotating shaft, a plurality of mixing rods are connected to the cross rod, sliding grooves are symmetrically formed in the inner walls of the left side and the right side of the mixing drum, and a discharging opening is formed in the bottom of the mixing drum. The concrete mixer has the advantages of being reasonable in structure, large in mixing area, uniform in mixing and beneficial to improvement of product quality and market competitiveness.