In order to study the difference of pore structure and thermal conductivity of foam concrete with different densities， X-ray computer tomography（X-CT） was used to scan foam concrete samples of four densities， and the three-dimensional reconstruction of pore structure of foam concrete was realized. Based on the pore characteristics and distribution of the sample， the foam concrete models of four densities were established by using the randomly generated code of Matlab， and the steady-state heat transfer was simulated in Comsol finite element software. The results show that the pore size distribution of foam concrete approximately obeys lognormal distribution. The porosity and pore diameter decrease with the increase of density， and the pore shape tends to be spherical. The internal heat transfer of foam concrete is mainly carried out in the cement matrix. A small part of the heatflow will pass through small pores， while large pores increase the conduction path of heat flow， which has a great influence on the thermal conductivity of foam concrete.