The invention discloses a stirring machine for site construction of an external wall. The stirring machine comprises a rack; the rack is provided with a stirring barrel; the stirring barrel is provided with a feed inlet and a discharge outlet and is internally provided with a rotary shaft; the rotary shaft is connected with a motor and at least provided with a stirring mechanism; the stirring mechanism comprises two arc-shaped fixed blocks matched with each other; the two radial ends of each arc-shaped fixed block are provided with convex blocks; the convex blocks are provided with thread holes; bolts penetrate through the thread holes so that the two arc-shaped fixed blocks can be defined to be of a circular ring structure; and the outer walls of the arc-shaped fixed blocks are provided with connection rods, and the connection rods are provided with stirring blades. According to the stirring machine for site construction of the external wall, the stirring mechanism is detachable by arranging the two arc-shaped fixed blocks matched with each other, and the problem that stirring blades of existing stirring devices are difficult to replace is solved.