In this paper we study the complete space-like λ-surfaces in the three dimensional Minkowski space R31. As the result, we obtain a complete classification theorem for all the complete space-like λ-surfaces x : M 2 → R31 with the second fundamental form of constant length. This is a natural extension to the λ-surfaces in R31 of a recent interesting classification theorem by Cheng and Wei forλ-surfaces in the Euclidean space R3.