Abstract: :In pile static load test, effectual isolation method must be adopted to wipe off the unemployed segment pile shaft resistance in order to get the bearing characteristics of a single pile at the actual working elevation, when there is a relatively long unemployed pile segment.It is illustrated with an engineering test example in Beijing that double steel casing method is an efficient way to wipe off the unemployed segment pile shaft resistance.Farther, by comparing the tested result of thework pile, it shows that there will be a risk in directly applying the test result data in project, and the effect of overburden on the test results should be considered in pile foundation design