The rockbolt functions as a main support, which restricts enlargement of the plasticity area and increases stability in the original ground around tunnels, and prevents a second deformation of an excavated surface by supplementing vulnerability arising from opening of the excavated surface. System bolting is generally applied if ground conditions are bad. System bolting is generally installed perpendicular to the excavation direction in every span. If a place is narrow, or it is difficult to insert bolts due to construction conditions, it may be connected and used with short bolts, or installed obliquely. In this study, laboratory model tests were performed to analyze the effect of the ground being reinforced by inclined bolts, based on a bending theory that assumes that the reinforced ground is a simple beam. In all test cases, deflections and vertical earth pressures induced by overburden soil pressure were measured. Total of 99 model tests were carried out, by changing the installation angle of bolts, lateral and longitudinal distance of bolts, and soil height. The model test results indicated that when the installation angle of bolts was less than $75^{circ}$, deflections of model beams tended to increase rapidly. Also, the relaxed load that was calculated by earth pressure was rapidly increased when the installation angle of bolts was less than $75^{circ}$. However, the optimum installation angle of inclined bolts was judged to be in the range of $90^{circ}{sim}75^{circ}$. Also, as might be expected, the reinforcement effect of bolts was increased when the longitudinal and lateral distance of bolts was decreased.