There are problems of inter-fracture interference and unbalanced modification in multi-cluster fracturing within the horizontal well section. Quantifying the degree of multi-fracture interference within the section is crucial for optimizing the fracturing plan and evaluating the effect of fracturing modification. An intra-segment multi-fracture propagation model of fluid-solid coupling was established based on the phase field method. Based on this model, the influences of cluster number and fracture spacing on fracture propagation patterns were studied. Innovatively, it is proposed to take the deflection distance, the area of the compression/tension zone and the pressure difference of the fluid in the fracture as indicators to quantify the degree of inter-fracture interference. The research results show that the increase in the number of clusters within the segment significantly inhibits the propagation of the middle fracture, resulting in a decrease in the deflection distance of the fractures on both sides. When the fracture spacing increases, the deflection degree of the fractures on both sides decreases. Both the increase in the number of clusters and the fracture spacing significantly reduced the area of the compression zone. The fluid pressure difference within the fracture increases with the increase in the number of clusters (an increase of approximately 3.28 MPa from 3 clusters to 5 clusters), but decreases with the increase in the fracture spacing (a decrease of approximately 7.26 MPa from 15 m to 25 m). The research reveals the multi-fracture competitive propagation mechanism, proposes that the optimization of segment clusters needs to balance the fracture propagation range and the stress interference effect, and is verified in combination with on-site construction cases, providing a theoretical basis for the design of fracturing parameters in horizontal wells.