To study the influence of specimen thickness on the collapsibility indexes of loess, a series of collapsibility tests on loess specimens at different depths (from 1 m to 20 m) in a certain area of Xi'an were carried out using conventional high-pressure and modified consolidation apparatus, respectively. The results of indoor collapsibility tests on loess specimens with thickness of 2 cm and 8 cm were compared and analyzed. The conclusions showed that the collapsibility coefficients of specimens with different thickness are similar when the collapsibility of soil is weak or the pressure is small. The difference between two specimens is more and more obvious with the increase of pressure when the collapsibility of soil is strong, and the collapsibility coefficient of 8-cm specimen is much larger than that of 2-cm specimen under the same pressure. The stronger the collapsibility of loess, the greater the influence of specimen thickness on the collapsibility indexes (collapsibility coefficient, self-weight collapsibility coefficient, and initial collapsibility pressure). This conclusion can provide a basis for the adjustment of specimen thickness in indoor collapsibility test.