The buckling behavior and critical value are analyzed to explain the mechanism of the lateral buckling. Moreover, a 3D numerical model of four tensile armor wires with symmetrical arrangement is established with the interaction between armor wires and inner structure. The lateral buckling is discussed through a relationship between critical value and axial displacement. Then the sensitivity of critical value on friction coefficient is figured out. The results show that the lateral buckling resistance of tensile armor wires performs better with the friction coefficient in the range of 0.25 to 0.3. Finally, this research provides mechanical support for the lateral buckling resistance design of the unbonded flexible pipe.