Abstract: he precipitation of paraffin, which attracted much attention among oil engineers, caused a lot of damage during the whole oil-gas production segments. However, it is unavoidable for paraffin precipitating when producing oil. This paper used rock-capillary model to simulate the formation pore volume, and derives the variation equation between paraffin precipitation and formation parameters using the correlation among surface area to volume ratio, porosity and permeability, etc. Through a practical calculation we made a conclusion that porosity and permeability have declined separately after the precipitation of paraffin.