We experimentally investigate the effect of the hopper angle on the fl ow rate of grains discharged from a two-dimensional horizontal hopper on a conveyor belt. The fl ow rate grows with the hopper angle, and finally reaches a plateau. The curve feature appears to be similar for different orifice widths and conveyor belt-driven velocities. On the basis of an empirical law of fl ow rate for a fl at-bottom hopper, we propose a modified equation to describe the relation between the fl ow rate and hopper angle, which is in a good agreement with the experimental results.