As an analogy to Gopakumar-Vafa conjecture on CY 3-folds, Klemm-Pandharipande defined GV type invariants on CY 4-folds using GW theory and conjectured their integrality. In this paper, we define stable pair type invariants on CY 4-folds and use them to interpret these GV type invariants. Examples are computed for both compact and non-compact CY 4-folds to support our conjectures. 1 0.4. Verifications of the conjecture I: compact examples. We first prove our conjectures for some special compact Calabi-Yau 4-folds.Sextic 4-folds. Let X ⊆ P 5 be a degree six smooth hypersurface and [l] ∈ H 2 (X, Z) ∼ = H 2 (P 5 , Z) be the line class. We check our conjectures for β = [l] and 2[l]. Proposition 0.3. (Proposition 2.1, 2.2) Let X be a smooth sextic 4-fold and [l] ∈ H 2 (X, Z) be the line class. Then Conjecture 0.1 and 0.2 are true for β = [l] and 2[l].Elliptic fibrations. We consider a projective CY 4-fold X which admits an elliptic fibration π : X → P 3 ,given by a Weierstrass model (2.1). Let f be a general fiber of π and h be a hyperplane in P 3 , set B = π * h, E = ι(P 3 ) ∈ H 6 (X, Z), where ι is a section of π. Then we have