Abstract: The examination methods of the discharge capacity of plastic drainboards and the equivalent opening size of filters in the current Quantity Inspection Specifications for Plastic Drainboard are discussed. The differences of the discharge capacity of plastic drainboards produced by two kinds of examination methods (one is soil media method and the other is rubber membrane method) are analyzed, and the shortcoming of the correction of the temperature is also analyzed. Finally, the rubber membrane method is suggested to examine the discharge capacity of plastic drainboards, and the filter's equivalent opening size O_(95) of the plastic drainboard is suggested to be less than 0.075 mm.