Abstract: Aiming to solving the problem of disaster caused by instability determination of different sizes coal pillars in the process of remining residual coal, uniaxial loading experiments were carried out on coal and rock specimens with different high-diameter ratios to study the effect laws of failure forms, stress-strain curve forms, peak strength, peak stress and elastic modulus of coal and rock specimens with different high diameter ratios.The results show that with the decrease of the ratio of height to diameter, the failure forms of the specimens change from shearing failure to complex failure.The peak stress σ_maxand the peak strain ε_Pincrease by power function model with the decrease of the height to diameter ratio, and there is a functional relationship between them with the increase of the height-diameter ratios:ε_P=0.218σ_max-2.465.The elastic modulus and secant modulus decrease with the decrease of the ratio of height to diameter.Both are quadratic function relationship each other.0.8 and 1.5 are the key aspect ratios that cause the change of change rate of mechanical parameters of coal and rock specimens.When the aspect ratio is less than 0.8, the mechanical parameters change obviously, however, when it is more than 1.5, the change tends to slow down.The above-mentioned results can be applied to the stability determination of coal pillar with different ratio of width to height, which improves the safety of remining coal.