Electrical impedance tomography (EIT) is a medical imaging modality that is used to compute the conductivity distribution through measurements on the crosssection of a body part. As a result the boundary shape of the organisms is different, building different boundary shape will affect the precision and clarity of imaging, so to build a suitable boundary shape is the precondition of solving the forward problem of EIT, especially in the chest. According to the actual visual effect, the elliptical geometry conforms to the chest boundary shape, due to the construction and finite element method of a circular shape is quite mature, this article uses conformal mapping method convert circular to elliptical geometry, and then analyzes and compares the two shapes respectively with the original chest geometry, the results showed that to build elliptical geometry in analyzing the forward problem of chest structure has higher precision, in solving the inverse problem has smaller reconstruction error.