Abstract: The k-type pseudo null helixes in the 3D Minkowski space are defined， and then the geometric properties of such kind of curves are discussed via the new defined structure functions of pseudo null curves. Firstly， the structure functions of pseudo null curves are defined according to the concept of pseudo null curves， then the representation forms of pseudo null curves are obtained and the relationship between the structure functions and the curvature functions of pseudo null curves is revealed by the defined structure functions. Secondly， the geometric properties of k-type pseudo null helixes in the 3D Minkowski space are discussed. The results show that any pseudo null curve is a 1-type pseudo null helix， there does not exist 2-type pseudo null helix， and a differential equation satisfying the curvature function of a 3-type pseudo null helix can be obtained. Meanwhile， the expressing forms and types (spacelike axis， timelike axis， lightlike axis) of axes for k-type pseudo null helixes are given.

Key words: Minkowski space, pseudo null curve, k-type pseudo null helix, structure function, curvature, axis