Abstract: In order to study the propagation law of multiple cracks under different rock mechanical properties, considering the influence of fluid flow on crack propagation and rock deformation, a mathematical model for vertical propagation of hydraulic fracturing cracks was established based on the extended finite element method. The effects of rocks with different mechanical properties on the injection pressure, injection point width, crack deflection, and crack spacing of multiple cracks were obtained. The results show that with the enhancement of elastic modulus and tensile strength, the crack propagation length and pore pressure increases under the same fracturing time. The equivalent displacement of rocks increases with the decrease of rock elastic modulus and tensile strength, and is positively correlated with the number of cracks. Moreover, as the number of cracks increases, the trend of the increase in equivalent displacement of rocks becomes more pronounced. With the enhancement of elastic modulus and tensile strength, the effect of crack spacing on pore pressure at the injection point is not significant. When the spacing between cracks increases to a certain extent, the stress interference between cracks decreases, and cracks do not deflect. This study has certain reference significance for optimizing the cluster spacing of hydraulic fracturing construction process under different lithology.