The technique of hydraulic fracturing has been originally developed assuming cohesive rocks. On the other hand, recent trends of petroleum industry is directed toward unconventional resources such as heavy oil and methane hydrate in weakly consolidated to unconsolidated sands. Thus we examine experimentally and theoretically the hydraulic fracturing behavior in unconsolidated sands. Moreover, an original Distinct Element Method (DEM) code corresponding to unconsolidated sand was developed, and the flow-coupled DEM simulations for the hydraulic fracturing were performed. By comparing experimental and numerical results, the mechanism of the hydraulic fracturing, such as cavity expansion, in the unconsolidated sands was discussed in detail.