In this paper, a facilitated cell model has been built to analyze the electromagnetic pulses (EMP) induced transmembrane potentials. The analysis shows that the athermal biological effects are caused by micropores on the membrance, not directly by transmembrane potentials. These micropores are enlarged by weak transient EMP and finally lead to membrane openings to make ions cross. The electroporation effects are used to explain the specific response of biological cells to transient EMP.