For validating an invented joint for sectional wind turbine blades, a separated composite box-beam with new characteristics was designed and fabricated for the first time,which were composed of metal bushings and stud-bolts joining together.Modal and static experiment under extreme bending loads were carried out on this 13.5 m sectional beam, for more detail information about joint bolts, numerical model combined shell and solid elements was constructed to help the test, good agreement of natural frequencies and deflections between finite element and test validated the model proposed by authors, output results also indicated that nonlinear effect of large deflection on the beam was not remarkable, stress concentration of beam spar adjacent to joint section was serious which should be paid closely attention.Under extreme bending loads, loads of joint bolts connecting tensile spar cap of beam nonlinearly increased with bending loads, which was generally avoided in engineering design.