Abstract: This paper studies the effect and fluid-solid coupling mechanism of hydraulic fracturing in rock samples with different compactness. It prepares two kinds of remolded samples with different compactness. The acoustic data and void ratio of two kinds of samples are obtained by the acoustic wave & true density test system. Combined with the hydraulic fracturing monitoring system under triaxial loading, the hydraulic fracturing tests of samples of different fluid rates under certain formation pressure are simulated. Analyzing the acoustic data obtained from the acoustic test shows that the density of the samples is different and the wave velocity is positively correlated with the compactness of the samples. There is lower compactness with higher porosity. In the hydraulic fracturing test, the crack propagation direction of the compact specimen is parallel to the maximum principal stress. The variation trend of the hydraulic pressure curve is as follows. At low compactness, the time to reach the peak pressure is shorter than the back part of the peak, while the high density sample is opposite. The fracture pressure of low compactness specimen is lower than the peak value of hydraulic pressure curve in hydraulic fracturing, and that of high compactness sample is the same value. Combined with above analysis and non-confining pressure test of high compactness specimen, it can be concluded that the change of low flow rate has little effect on the crack propagation direction of the specimen with higher density and it's seepage effect is weak. The stress concentration effect is obvious in the samples without confining pressure and the samples with low compactness, which indicates that the stress concentration phenomenon in the hydraulic fracturing test is obvious in the samples with low density, that is the seepage flow rate is larger and the seepage effect is stronger. The seepage of hydraulic fracturing is positively correlated with the flow rate of injection and the low density sample has remarkable performance.