The invention relates to a laser frequency stabilizing device for an atomic clock, wherein a laser, a 1/2 wave plate, a first polarization splitting prism, a magnetic shielding box which is internally provided with a reference atom source and a third photoelectric probe, a first 1/8 wave plate, a partial reflection mirror, a second 1/8 wave plate and a second polarization splitting prism are orderly arranged on a bottom plate from the left to right in the horizontal optical axis direction; connecting holes are formed on the magnetic shielding box, and light guide holes are formed on two sidewalls in the same horizontal optical axis direction; a first photoelectric probe is arranged in the outgoing direction of the second polarization splitting prism on the bottom plate, and a second photoelectric probe is arranged in the reflecting direction; a subtracter connected with the first photoelectric probe and second photoelectric probe via the leads, a proportional-integral differential controller connected with the subtracter via the leads, and a microprocessor connected with the third photoelectric probe via the leads are arranged on the bottom plate; and a controllable switch which is connected with the laser, the microprocessor and the proportional-integral differential controller via the leads is arranged on the bottom plate.