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It has been recently reported that the porosity and the density and so forth in the surficial marine sediment vary largely with the depth. The characterisitics of acoustic wave reflection from such transition layer of the surficial marine sediment seem to be very different from that from homogeneous sediments. In this study, the incident angle dependence of the reflection coefficient for the transition layer of the surficial marine sediment model is calculated using OASES (Biot-Stoll model). The effects of the transition layer, and the frequency dependence of the reflection coefficient characteristics are investigated. Next, the characteristics of the incident angle for the reflection coefficient are measured in water tank and in situ. Beach sand (fine sand) are used for water tank measurements, and in situ measurements are done in a very fine sand bottom The operating frequency is 150 kHz. The incident angle are 0, 20, 50, and 60 degrees. Die measured results are compared with the calculated results using OASES (Biot-Stoll model), and the effects of the transition layer on the characteristics of the reflection coeffieint are investigated.