Abstract: In view of the characteristics of expansive soils and the situation that CBR(California Bearing Ratio) of expansive soils seldom satisfied the requirements of current specifications for the design of highway subgrades(CBR≥3%),from three aspects,i.e.,soaking method of prepared samples,surcharge during soaking period and moisture content of prepared samples,the irrationality of using standard CBR test to estimate the bearing capability of expansive soils was extensively analyzed.According to the actual condition that the envelope and water barrier method was used to successfully build test embankments with core filled with expansive soils,a modified CBR test method to evaluate the real bearing capability of this kind of special soils was suggested and studied.The method included preparing samples with heavy compaction standard and the optimum moisture content in light of wet compaction test,changing the water soaking method from the top to the lateral of samples,meanwhile,increasing the load on the samples during the soaking period.The rationality and feasibility of the modified method were verified by comparing the test results of routine and modified CBR tests on six samples including expansive soils and nonexpansive soils.The evidence was provided for the construction of embankments in areas of expansive soils where the expansive soils with different swelling potentials could be directly used to fill the lower part of the embankments.