In order to study the influences of rigid,half-rigid,and flexible boundaries on test results,unilateral loading tests on coarse-grained soil,with invariable horizontal stress and increasing vertical stress,were performed using the TSW-40 true triaxial apparatus developed by Hohai University. The results show that the restriction of the rigid boundary is clear on a cubic sample with the depth-width ratio of 1:1;using a half-rigid boundary on the top of a sample,with the rigid boundary in the vertical direction and the flexible boundary in the horizontal direction,can remarkably decrease the restriction of the boundary on the sample;the restriction of the rigid boundary on a sample can be effectively decreased by increasing the depth-width ratio of the sample;and half-rigid compound blocks and flexible water bags have a lesser influence on the test results.