The present work has explained a long-standing discrepency between theory and experiment: the broadening of the distances at which Rydberg atoms ionize over a metallic surface. The uneven surface potential distribution on a template-stripped gold surface evaporated on mica is measured with Kelvin probe force microscopy. The stray fields generated by the surface potential are calculated. Simulation with C++ and Matlab predicts how stray fields affect the ionization of Rydberg state atoms near a gold surface. The predicted survival probabilities for different n levels and different incident angles provided by the simulations are then compared with experiments, which shows surprisingly good agreement. Although metallic surfaces are approximately ideal equipotentials in the macroscopic world, Rydberg atoms demonstrate the important role stray fields play in the microscopic world.