The selection of test points is the basic problem of analog circuit fault diagnosis.How to find the least number of test points to isolate all the fault circuit has become the focus of the study.Commonly used test point selection methods are mostly fault dictionary method.The study found that if a particular fault in the circuit can only be isolated by a special test point，then taking this special test point out can greatly simplify the fault dictionary, by finishing the selection of the remaining valid test points and the removal of redundant test points, the best set of test points can be chosen. This method is called special test point isolation algorithm. Through compared experiment, it is found that the proposed algorithm balances the requirements of time and accuracy in test point selection. What is more, it has a higher efficiency.