The invention discloses a volume alternating fracturing method of a horizontal well in an experimental shale reservoir. The method comprises the following steps: collecting the stratum parameter, the natural fracture parameter and the hydraulic fracture basic parameter of a reservoir; establishing stretching, shearing and pass through failure criterions of a natural fracture when a hydraulic fracture and the natural fracture are interacted, and quantitatively analyzing the influence on the natural fracture failure by a horizontal principal stress difference; establishing a hydraulic fracture induced stress calculation model, and computing the influence on the induced stress of a middle perforation cluster fracture elongated area by gaps among different perforation cluster fractures and fracture extended lengths; optimally selecting a shale reservoir horizontal well volume fracturing perforation cluster gap and perforation cluster extended lengths at the two ends, so as to promote a middle perforation cluster hydraulic fracturing fracture to be extended and interactively produce stretching, shearing and pass through failure modes with the natural fracture at the same time to form a complex fracture. According to the method, induced stress field produced through the extension of the hydraulic fracture, perforation gaps within the same fracturing section and the extended fracture lengths are organically combined, and the horizontal well volume fracturing technology is properly perfected.