Abstract: A 3-dimensional Ising model is simulated with Monte Carlo importance sampling method. Statistical values of energy, strength of magnetization, specific heat and rate of magnetization of spin links as well as their standard errors (uncertainties) are measured. 3-dimensional Ising model shows spontaneous magnetization with no exterior magnetic field. Critical point of phase transformation is at J/(k_BT_c)=0.222 0 or T_c=4.500 0. Phase transformation at high temperature disappears with exterior magnetic field. Relationship between physical quantities, temperature and exterior magnetic field is investigated and analyzed.