Abstract: The main problem of decompaction correction is how to found a reliable porosity depth function or density-depth function which expresses the compaction process of clastic rock. Because the present day relationship between porosity and depth usually is measured from different layers in one well or poly wells, it couldn't reflect the compaction path of a given layer during burying history. A function found on the data of porosity depth or density-depth from a given layer in one well or poly wells could be more reliable so that it can figure out a satisfying decompaction thickness. Because the grain density of rock keep a constant in any depth, the relationship between porosity depth function and density-depth function should be a linear complement and the initial value and compaction coefficient in the Athy's porosity depth function also could be resolved from two or more sets of porosity depth and density-depth data measured in the same layer.