Abstract:Shallow refraction is often used in seismic static correction data collection and engineering geology investigation. However,the existence of subtle layer causes severe error in shallow refraction interpretation,whieh was neglected by people.Rz the range function of a subtle layer is introduced here. The relation between subtle layer range and its formation parameter,overlying formation or underlying formation parameter is analysed by making forward modeling. The general condidons of a subtle layer existence are summarized briefly. The error is analysed which can be brought when people use usual methods to interpret the shallow refraction data in the area where subtle layer occurs. The article describes two methods for discovering subtle layer:interpolation method and mean velocity method. The author also points out the matters needing attention in collection and interpretation of shallow refraction data. It is illustrated that the interpretation method in this article favors removing the influence which subtle layer causes for shallow refraction interpretarion accuracy.