This paper presents an analysis in attachment spacing of tower cranes. Both the support spacing under the rigid support and the flexible support are obtained for this purpose. For deriving the rigid support spacing, differential equation is used. The principle is used for calculating the support spacing, which the extended segment has the same Euler critical force with the independent segment. The flexible support distance is obtained by setting the integrated stiffness matrix zero, which is equivalent to structural instability. The order of the overall stiffness matrix is big when the tower crane is attached many times. In order to calculate more convenient for solving the matrix determinant, a transfer matrix method is adopted. To verify the influence of the flexibility caused by the support device, an example is carried out by both rigid and flexible support situations for this purpose, and the support spacing is computed numerically. Numerical results for the support distances of a tower crane will be presented and discussed.