Computer simulations are performed to investigate the effect of opening angle on dilute-dense flow transition in a two-dimensional granular flow. Two methods, i.e. the fixed inflow rate and the fixed particle number, are adopted. Both results show that larger opening angle results in an increase of maximum outflow rate in dilute-dense flow transition when the opening angle is larger than zero. When granular flow keeps a dilute flow, the outflow rate is irrelative with the opening angle. When the flow becomes a dense flow, the dense flow rate inereases with opening angle increasing. Further studies show that the granules flow out with a higher velocity when the opening angle increases. The linear relationship between maximum outflow rate and granule flow velocity is observed.