For uniaxial tension test result can be largely affected by sample forms and tensile length, both of which were quite different in the current experimental research, the study developed a set of dumbbell uniaxial tensile sample preparation mould, for preparing samples with different tensile lengths. Sample preparation mould consists of two horizontal loading section moulds, two vertical stretching section moulds and a sample preparation base plate, with dovetail slot connecting loading section moulds and stretching section moulds. Based on this, the uniaxial tensile test of clay specimen was carried out to analyze the tensile properties of clay, and discuss the influence of sample forms and tensile length on the failure mode, tensile strength and peak displacement. The results showed that end relaxation and stress concentration issues can be avoided in the tensile process for applying dumbbell specimens and the tensile fracture plane occurs in the range of effective tensile length; failure mode of clay is not pure brittle failure, but there is a softening phrase after tensile strength; with the increase of tensile length, uniaxial tensile strength decreases but peak displacement raises, and both show a logarithmic relation with tensile length.
