The evolution processe of laser induced plasma shielding shock wave is studied. The temporal and spatial evolution processes of the plasma and shock wave are investigated, when nanosecond laser focused on the surface of the aluminum target through the glass, using optical shadow imaging diagnostic techniques. The collision time of the shock waves increases with the distance between the glass and the aluminum target. Experimental results demonstrate that the shock waves do not interact with each other but interact with the plasma in the collision, and the shock wave front distortion or even broken will exist, the shock wave is shielded by the plasma. And the physics mechanism of plasma shielding shock wave is analyzed.