The recognizing sequence of restriction enzyme includes palindrome and nonpalindromic, and DNA is double helix complementary strands. So the recognizing sequences of palindrome enzyme in two strands of DNA were identical,and can be considered of one sequence. But for nonpalindromic restriction enzyme,the recognizing sequences of two strands of DNA were not identical. Therefore the true recognizing sequences are not only one. In this experiment,an enzyme cleavage reaction was carried out which confirmed that the true recognizing sites/sequences of nonpalindromic enzyme are two instead of one.