Abstract: The vertically focused monochromator of the neutron powder diffractometer was simulated using Monte-Carlo method. The effective dimension, curvature radius and tilting angle of monochromator are obtained. The intensity gains and the neutron intensity distribution at sample position are also given comparing to flat monochromator, the result is that there is not evident intensity gain when use the vertically focused monochromator instead of the flat monochromator at more sample because of the limit of hole dimension. Only when little sample can be obtained there is more evident intensity gain.