Abstract: In view of the deficiency of the existing geotechnical tension test devices, a set of horizontal direct tension test device is developed. The test device consists of tensile loading system, digital control hydraulic system and data acquisition analysis system. Using the test device, direct tension tests on easy formation materials can be carried out, and tensile strength and tensile stress-strain curve can be precisely obtained. The loading clamp of device can solve the connection problem between the test specimen and the tensile device. The test device can control test tension continuously and accurately. The post-peak tensile stress-strain curve of materials can be obtained. Using this test device, direct tension tests on clay, iron crystal sand similar materials and cement mortar are carried out. The results show that the tensile strength of clay decreases with its moisture content linearly and the peak tensile strain of clay increases with its moisture content linearly when the dry density of clay remaines unchanged. When the tensile stress of clay reaches the peak stress, the clay specimen will not be destroied suddenly. At this time, the clay specimens still have bearing capacity. The tensile strength of iron crystal sand similar materials will rise as the concentration rosin alcohol solution increases. As the cement-sand ratio increases, the tensile strength and tensile modulus of elasticity of cement mortar will increase accordingly.