The program for one-dimensional equivalent linear soil seismic response is verified using the underground and surface seismic records of the KiK network in Japan.The results show that，in the range of small soil deformations，the calculated ground motions are consistent with the actual motions for the sites where the stiffness of soil layers increase with depth，but not for the sites with soft or hard interlayers.Accordingly，this paper presents a method to study the effects of soft and hard interlayers on ground motions.As a reference，the interlayer is replaced by a normal soil layer to meet the condition of increasing stiffness.Then，the surface seismic response excited by the actual underground motions is computed using the program.Comparing the computed motions and the actual motions on the surface，conclusions can be drawn.Some representative sites are studied in this paper.The results show that the effects of soft and hard interlayers on ground motions are consistent；there is an amplification of high-frequency motions if the interlayer is shallow，but there is an action of seismic isolation to high-frequency motions if the interlayer is deep.