The most difficult problem in surface intersection is to determinate all the initial tracing points. Collinear normal line is a power tool for solving this problem. A lemma about the existence of collinear normal line between two tori is presented, based on this lemma an algorithm for finding all the initial tracing points is implemented, numerical examples show that it is robust and efficient. The most difficult problem in surface intersection is to determinate all the initial tracing points. Collinear normal line is a power tool for solving this problem. A lemma about the existence of collinear normal line between two tori is presented, based on this lemma an algorithm for finding all the initial tracing points is implemented, numerical examples show that it is robust and efficient.