To investigate the stability of the new full steel undersize-log formwork with early-removal substructure, 4-bay-5-row which were made up of the logs and steel tubes as a test unit were prepared to study the compressive failure test. The loading patterns and time which affected the substructure were considered, the supports force and deformation were analyzed, and the failure modes that were out-plane bucking and strength failure were observed in some members. The experimental results show that the pouring concrete actual speed should not too fast, and speeding up the turnover time of this formwork is available to reinstate the stress of this log. The members during pour concrete should be monitored. The structural measures and horizontal restraints of joints are absolutely essential, and the logs which are serious imperfection can obviously decrease the stability of the new formwork, so that attention should be paid to the weak parts of the installation location.