The invention relates to a method for fracturing a horizontal well through penetrating shale layers. The method comprises the following steps: (1) quickly starting a fracturing fluid conveying device; (2) injecting a large quantity of fracturing fluid; (3) injecting a large quantity of prepad fluid for expanding gaps; (4) injecting small-size propping agents; (5) stepwise increasing low sand ratio. The method successively achieves the purpose of communicating upper and low reservoirs through penetrating shale layers to fracture, ensures that the successive fracturing construction in the horizontal well with sand shale interbeds, transforms upper and lower sand shale hydrocarbon reservoirs to a greater degree, improves the construction success rate and the effective mining-employed reserves greatly, and obtains remarkable economic benefits. The method is reasonable in design, simple in construction technology, simple and convenient to operate, high in fracturing construction successive rate, and remarkable in construction effect, and has wide application prospects in the fracturing process of the horizontal well with the sand shale interbeds..