Some key parameters of illuminating beam and the influence on imaging quality are investigated via ptychography in visible light band. The influences of overlap ratio, size and shape of illuminating beam on imaging quality and their relationship are studied using ptychographical iterative engine algorithm. The simulation results show that the overlap ratio of illuminating beam is a main factor influencing imaging quality. Shape of illuminating beam mainly influences the convergence of ptychography. And the size of illuminating beam less influences directly the imaging quality and convergence. Therefore, the simulation results play an important theoretic guiding role in optimizing the beam parameters in visible light, the X-ray and electronic band and other bands.