A 4-layer sphere model of human head is built.Layers from outside to inside represent scalp,skull,CFS and brain,respectively.The point current source placed on the outmost layer is regarded as boundary condition.A method of separation of variables is used to solve the equations.Potential distributions with different injecting angles are shown.We simulate conductivity distribution of brain tissue, and plot real and imaginary potentials at nine points on the outmost layer.As conductivity of brain tissue changes,the real potentials vary greatly than the imaginary parts.Frequency characteristic is simulated,and the result shows that the imaginary potentials on the outmost layer is influenced mostly by frequency.These can be used in analyzing head EIT problems and improving the Back-projection Algorithm.