The measurement of soil infiltration has long been a great concern of scientific researches and applicants. Ring infiltrometeris a widely-applied instrument for soil infiltration measurement. Rain simulator and double ring methods are the common methods for measuring soil infiltration, but the disc infiltrometer is widely for determination of saturated hydraulic conductivity. Numerous reports indicated that the most reliable results measured by the ring infiltrometer in the saturated hydraulic conductivity. This indicates the drawbacks of the ring infiltrometer. The gaps between the ring and the soil during the ring being inserted into soil produces a passage for preferential flow to cause much higher infiltration rate. The relative long time interval between each measurement is another reason to produce higher measured infiltration rates, which is illustrated by numerical computational procedures. Both the time moment at which the computed infiltration rate is assigned to and the length of time step have their impacts on the measured soil infiltration curve. The errors caused by these factors, especially at the beginning of infiltration are illustrated. 