The invention discloses a cement mixer. The cement mixer comprises a power source, wherein a stirring rod is fixedly connected to the left end of the lower surface of the power source, a powder screening box is fixedly connected to the left side of the outer surface of the stirring rod, a stirrer is fixedly connected to the bottom end of the stirring rod, a support is fixedly connected to the left side of the outer surface of the powder screening box, the bottom end of the support is fixedly connected with a base, the top end of the base is fixedly connected with the bottom end of the stirrer, and a cement outlet is formed in the right end of the base. When the cement mixer is used for producing cement, coarse cement is poured into the powder screening box, then the machine is started, the power source enables the stirring rod to rotate violently, the stirring rod stirs, crushes and refines the cement, the yield is improved, large particles and cement blocks in the cement can be left in the powder screening box, cannot pass through the cement outlet, and then need to be re-ground, therefore, a user can quickly and efficiently find out bad cement by using the machine, and production is improved in a targeted manner.