On the basis of Van der Pauw method，the Van der Pauw formula is simplified. Under the critical condition，the form of Van der Pauw formula is preserved，namely，the constant of the equation is modified and critical value is calculated. The complete method of measuring resistivity of single hole material is summarized. For the porous materials，the quantitative formula of field strength，current and resistivity are deduced. The problem is solved by software simulation，fitting quantitative and analogy method to find the distribution of field intensity and current value. The condition of application of the Van der Pauw method is extended.