In order to study the rest time and the reducing rate of liquid level on thickness and uniformity of polystyrene（C8H8）filters, C8H8 filters are made by dip-coating and measured by Vecco Dektak6.0 Stylus Profiler. The interpolation fitting method is introduced to research the relation of C8H8 filters with the rest time and the reducing rate of liquid level. It’s finding that the rest time and the reducing rate of liquid level have great influence on uniformity of C8H8 filter. With the shorter rest time and the smaller the reducing rate of liquid level, C8H8 filters have better uniformity.