Abstract: The steel tube structures are widely applied in building engineering because of their excellent mechanical properties． The design of the joints is an important part of the whole steel structure． An innovative test setup was developed and full scale experiments on 9 bottom chord splice joints with variable cross-section were fulfilled． The failure load and failure mode of those joints were obtained． Based on the rational simplified material nonlinearity and constraint condition，finite element model of the joints was established and solved． Comparing the experimental results with finite element analysis results，some beneficial conclusions were got．