Abstract: In order to study the influence of rock sample size on mechanical properties such as peak strength and acoustic emission space-time characteristics under different loading rates, numerical simulation and data fitting are combined to conduct uniaxial compression simulation tests on five groups of test pieces with different height to diameter ratios under different loading rates.The results show that the peak strength of rock is positively correlated with the loading rate, and negatively correlated with the ratio of height to diameter of rock sample.For the test pieces with different diameters, the loading rate plays a leading role in the rock size effect.When L/D ≥ 2, the rock sample size effect gradually weakens.At the same time, rock also has a significant influence on acoustic emission under different loading rates.When the ratio of height to diameter of the sample L/D is less than or equal to 2, the number of acoustic emission is more after the peak intensity.During the whole process, the number of acoustic emission increases gradually and then decreases gradually, showing a gradual change law.When L/D> 2 occurs, the number of acoustic emission is small, and obvious acoustic emission events occur after the peak intensity, which belongs to the change law of abrupt jump type, and has certain reference significance for predicting the arrival of uniaxial compression fracture of rock samples of different sizes by using acoustic emission characteristics.