As the cross-section of tunnels increases, the girder which has better load bearing capacity than the existing girder is needed. In this study, a new lattice girder which optimized the spider shape of lattice girder used as steel rib in NATM tunnel is suggested. Also practical indoor loading test which can model the difficult construction work section was conducted. By simulating the real tunnel and the load bearing capacity, the characteristics of the behavior of the tunnel lattice girder were analyzed. The developed girder has been found to have better load bearing capacity than the existing lattice girder from the results of indoor test using the straight specimen. The load bearing capacity was smaller in the straight specimens than the curved ones in the real scale test.