Warping degree of knot diagram was studied by Kawauchi and Shimizu . In this paper, we extend the notion and introduce a new approach to find warping degree  of a virtual knot diagram. We show that the sum of warping degrees of D and its inverse diagram  satisfy the inequality:  where c is the number of classical crossings of D. Furthermore, the equality holds if and only if D is an alternating diagram.

virtual knot, warping degree, knot diagrams, crossing number.