The invention relates to the technical field of building material processing, and discloses an automatic high-precision sand screening device for synthetic production of building materials, comprising a sand screening box, a cam connected to the outside of the output shaft, and sand screening boxes connected to both sides A pendulum, the lower end of the pendulum is connected with a U-shaped rod, the U-shaped rod is connected with a coil, the inside of the air injection device is provided with an air injection port, the lower end of the control device is connected with an air bag, and the inside of the moving block is connected with a magnetic block. The output shaft drives the cam to squeeze the screening plate intermittently, the gas in the sliding rod compression sleeve enters the air bag through the second one-way valve, the screening plate resets and hits the pendulum, the pendulum drives the U-shaped bar to vibrate, and the U-shaped bar The coil cuts the magnetic induction line to generate a current, and the current passes through the coil at the lower end of the coil to form a magnetic field. The magnetic field pushes the magnetic block to reciprocate in the sliding groove, and the gas in the air bag is ejected through the through hole. This structure solves the problem of the sieve plate of the existing sand screening device. Easy to block and low working efficiency.