Determination of water saturation is important for reservoir evaluation． When complex pore structures such as fracture and cavity are present in reservoir，Archie equation is no longer suitable． According to different models of pore structure division，the authors studied water saturation computation models． The results show that dual porosity system is divided into four models． The first model is based on dual laterolog，the second is Dual Porosity Ⅰ，the third is Dual PorosityⅡ，and the last one is based on the conductive pore． Besides，the triple porosity system is triple porosity model． Compute water saturation was using all the above five models in volcanic reservoir in Songnan gas field． The triple porosity system is the most suitable model for water saturation computation in complex pore structure volcanic reservoir．