Since there exists a distinct wave impedance surface between the cover and the medium-to-weak weathered rock, most energy of the incident wave was restrained in the cover and it is very difficult to stimulate effective elastic wave in the rock. Therefore, the response signal of the cavern or fault in the rock was too weak to record. Simplifying this kind of structure by two layer model together with the analysis and calculation of the wave equation, we can find the penetration laws of the incident energy on rock surface and then theoretically show that it is possible to choose little offset and near critical angle SVwave measuring in shallow or ultra shallow seismic survey. The consideration of as many factors as possible can lead to good ideas with which we can stimulate the most distinct response signal of the concealed targets.