Duty cycle of curved computer-generated hologram(CGH) was calculated for obtaining an optimal contrast of the interference fringe pattern in testing large aperture convex aspherical surface.The relation between the contrasts of the interference fringe pattern and duty-cycle was presented.Calculating duty cycle of curved CGH was described in testing a large convex mirror with Cr-glass CGH on curved surface.A curved CGH with duty cycle 0.2 was fabricated by using laser writing lithographic techniques.Analysis of experimental results shows the theoretical calculation agrees with experimental results at the contrast of the interference fringe pattern.