Based on Lanzhou South Ring Highway project,the field tests of piles were performed in a collapsible loess site by simulating the actual situation of the area"s annual rainfall.The tests were performed under pile load-free immersion state and in the consolidation process of loading and uninstalling test.The results show that the pile"s negative friction in the self-weight collapsible change value smaller and it"s sphere of influence in the 7M below the surface by simulating two discontinuity rainfall. There appear multiple peaks due to negative frictional resistance throughout the process of test, leading to more neutral points, for ease of design and construction, proposed the concept of equivalent neutral point.Equivalent neutral points are in the range of 0.257 to 0.40 times of the pile length.The locations of equivalent neutral points are smaller than the range proposed by <>.The results can provide references for the later design of pile foundation in Lanzhou area.