According to the on-orbit working characteristic of the coil-able mast structu re, the experimental investigation on the nonlinear buckling mode and the buckling l oad at different height and diagonal cable pre-load is carried out. Based on the geometric nonlinearity characteristic, the corresponding numerical simulation is developed by using arc-length method to obtain the nonlinear buckling mode of the structure. The analysis results show that: (1) the buckling mode and the buckling load obtained from numerical simulation agree well with those obtained from the experimental work, (2) the buckling mode of coil-able mast is closely correlative to its height and diagonal cable pre-load, and the bearing capability for the axial compression and bending can be significantly improved if the diagonal cable is under the tension condition. The result is expected to provide some valuable information for studying other similar structures in future.