In order to taking gun bullet mark feature availably, the way of conversion from 3-D bullet mark data to same form 0-1 feature point matrix is proposed. The mechanism of gun bullet mark is introduced, the process of bullet mark data getting by high-precision data-taking equipment is analyzed, Based of Hough space conversion model, the model of bullet mark feature line taking from same form 0-1 feature point matrix is made. The experiment of gun bullet mark feature line taking from 12 3-D bullet mark data of 6 guns is carried out. The test result shows that the method can effectively extract the feature line in right way.