Quantitative thickness estimation of thin-layer is a great challenge in seismic exploration,especially for thin-layer below tuning thickness.In this article,we analyzed the seismic response characteristics of rhythm and gradual type of thin-layer wedge models and presented a new method for thin-layer thickness estimation which uses relative peak frequency increment.This method can describe the peak frequency to thickness relationship of rhythm and gradual thin-layers in unified equation while the traditional methods using amplitude information cannot.What’s more,it won’t be influenced by the absolute value of thin-layer reflection coefficient and peak frequency of wavelet.The unified equations were presented which can be used for rhythm and gradual thin-layer thickness calculation.Model tests showed that the method we introduced has a high precision and it doesn’t need to determine the value of top or bottom reflection coefficient,so it has a more wide application in practice.The application of real data demonstrated that the relative peak frequency increment attribute can character the plane distribution feature and thickness characteristic of channel sand bodies very well. Quantitative thickness estimation of thin-layer is a great challenge in seismic exploration, especially for thin-layer below tuning thickness. In this article, we analyzed the seismic response characteristics of rhythm and gradual type of thin-layer wedge models and presented a new method for thin-layer thickness estimation which uses relative peak frequency increment. This method can describe the peak frequency to thickness relationship of rhythm and gradual thin-layers in unified equation while the traditional methods using amplitude information cannot. What’s more, it will not be influenced by the absolute value of thin-layer reflection coefficient and peak frequency of wavelet. The unified equations were presented which can be used for rhythm and gradual thin-layer thickness calculation. Model tests showed that the method we introduced has high precision and it does not need to determine the value of top or bottom reflection coefficient, so it has a more wide application in practice. a pplication of real data demonstrated that the relative peak frequency increment attribute can character the plane distribution feature and thickness characteristic of channel sand bodies very well.