Abstract: In order to solve the problems on loading capacity and stability of the U type steel support in the support of the soft rock roadway in deep mine, the mec hanics principle was applied to establish a structure mechanics model of the U type steel support.An analytic solution was obtained for the dangerous cross section loc ation of the U type steel support.The dangerous cross section of the U type steel support related to the cross section area and inertia moment of the support, the sectio n size and side pressure coefficient of the roadway was calculated.The bolt and channel steel were applied to the leg-locked support technology of the dangerous cross section of the U type steel support.The engineering practices showed that after the bolt and channel steel applied for the leg-locked to the U type steel support, the max convergence between the two sidewalls of the roadway was 125.62 mm only and the max convergence between the roof and floor was 172.36 mm.Thus the stability of t he surrounding rocks along the soft rock roadway in the deep mine was ensured.