This paper is concerned with the existence of positive solutions for the fourth order Kirchhoff type problem { ∆ 2 u − (a + b ∫ Ω |∇u| 2 dx)△u = λf (u(x)), in Ω, u = △u = 0, on ∂Ω, where Ω ⊂ R N (N ≥ 1) is a bounded domain with smooth boundary ∂Ω , a > 0, b ≥ 0 are constants, λ ∈ R is a parameter. For the case f (u) ≡ u , we use an argument based on the linear eigenvalue problems of fourth order elliptic equations to show that there exists a unique positive solution for all λ > Λ1,a , here Λ1,a is the first eigenvalue of the above problem with b = 0 ; For the case f is sublinear, we prove that there exists a positive solution for all λ > 0 and no positive solution for λ < 0 by using bifurcation method.