Abstract: The behavior of Paleozoic carbonate reservoir in Laiwu area is roughly known by pore geometry analysis,thin section cast observation and conventional petro-physical properties determination.There are more than 20 layers with thickness of 150m are favourable reservoir in this section.The types of the reservoir are:for Middle Cambrian,mainly dissolution vug type;for Ordovician,mainly fracture-dissolution vug type.There are 12 types of pore space:dissolution pore;intercrystalline pore;intercrystalline dissolution pore;intracrystalline dissolution pore;intergranular dissolution pore;intragranular dissolution pore;dolomite casting mould pore;structural fracture;interformational fracture;diagenetic fraccture;dissolution trace,stylolite etc.Secondary pore zones with developed dissolution pore,cavern,and crack were often formed near paleoerosional surfaces.There sre 6 secondary pore zones in this section.