In order to enhance the breakdown efficiency of perforation clusters in the process of staged multi-cluster fracturing in horizontal wells, a breakdown pressure calculation model of perforation clusters is established according to the induced stress of fracturing stage, the varying law of breakdown pressure of perforation cluster is analyzed based on the formation characteristics of multi-fracture synchronous extension in view of the stress resistance and effective net pressure between fractures. The results show that stress resistance exists while multi-fracture is extending synchronously in the process of staged multi-cluster fracturing in horizontal wells, the induced stress generated by the effective net pressure in last fracture of ahead stages will add up to the stage which to be fractured; perforation cluster furthest from the last fracture position has the minimum breakdown pressure, the difference between breakdown pressure of perforation clusters will increase with the extension of time, it is the best time to break all the perforation clusters at the early time of fracturing. The pump rate should be increased immediately to increase the bottom hole pressure by using the throttling effect of perforation; Big difference of breakdown pressure can be caused by little stress changing, so the change of breakdown pressure of perforation clusters which caused by induced stress must be paid more attention in perforation parameters design and fracturing parameters optimization.