Direct tensile (uniaxial tensile) test is the most accurate method to test the tensile strength and deformation modulus of rock. In order to overcome the problems of complex structure, unable to avoid bending and torsion of the current direct tensile test device, the equilateral angle aluminum is used as the centering bonding device, and the combination of aramid fiber rope and two rings is used as the stretching device. For the difference of rock sample diameter at different heights or in different directions, the centering bonding method of padding up with paper strips is proposed. Six strain gauges are pasted on the side of the aluminum bar. Several tensile tests show that the maximum eccentricity e is 0.24 mm, and the minimum eccentricity e is only 0.04 mm. It is verified that the centering bonding devices and method have good effect in direct tensile test. Then the tensile tests of two rock samples have been carried out, and the more accurate tensile mechanical parameters of rock can be get. The devices have the advantages of simple structure and low production cost, which is suitable for popularized application in uniaxial direct tensile test of rock.