For a vertically inhomogeneous layered model, Fourier-Bessel integration transform is applied to the equation of wave propagation, after that a synthetic seismogram can be obtained by a finite-difference iteration in the wave number domain. Due to the separation between space and time variables after the transform, such algorithm is of stable and wide feasible. In the present paper some models involving a lower velocity layer(LVL) and a higher velocity thin-layer are studied for comparison. Through an analysis for wave propagation in space and time domain, the processes of propagation and generation of several prominent phases are revealed. Computational results indicate that no matter how much the thickness of higher velocity layer is the reflection wave is still strong, while the initial head wave from the thin-layer is not obvious. It is worthwhile to point out that there exists one kind of converted head wave in the thinlayer. It is found that the upward propagation wave with strong energy is hard to be formed at the top of LVL, which means that there is rather serious uncertainty at inferring the depth of LVL.