In order to get the penetration effect of plum-blossom piles，a series of model tests of plum-blossom piles penetrating transparent soil was carried out. Combined with transparent soil and particle image velocimetry， based on the static pressure pile method，the displacement characteristics of soil around the plum-blossom pile in the process of jacked-pile penetration in different stages were studied. According to the cylindrical cavity expansion theory and the geometric characteristics of plum-shaped piles，a simple modified cavity expansion theory is pro? posed to compute the radial displacement induced by the pile penetration and the influence range of penetration effect of plum-shaped piles. At the same time，an analysis model of the penetration effect and cavity expansion of plum-shaped piles is proposed by using a numerical calculation method. By comparing the test results of the trans? parent soil test and the analysis results of the modified cavity expansion theory，the modified cavity expansion model is validated，and the penetrating process of plum-shaped piles and round piles with equal cross sections is com? pared. The results show that the soil compaction transition zone of a plum-blossom pile is about 1.5 times that of a circular pile with equal cross section，and the penetration effects of a plum-blossom pile are similar to those of tradi? tional equal section circular pile in cavity expansion area. The pile driving tip resistance，pile shaft and total resis? tance of tapered pile equal 1.0 times，1.38 times and 1.12 times of those of equal section circular pile respectively.