According to the internal consistency of the relative orientation and the epipolar geometry, this paper deeply analysis and discuss the relationship between relative orientation and the fundamental matrix based on the number of the relative orientation, degrees of freedom of the fundamental matrix and the corresponding relations between the parameter of them. Experimental results of images show that the proposed approach is practicable, gives great inspiration to the understanding of the mathematical principle about them, and the result of the Fundamental Matrix can convert to the result of relative orientation. After get rid of the error matching points, method of calculating the relative orientation through Fundamental Matrix can get higher precision results.