The invention provides a spacing method for horizontal well volume fracturing clusters. A finite element numerical simulation method is adopted, on the basis of ABAQUS finite element software, from the two aspects of reduction of the disadvantageous influence of the stress penumbra effect and utilization of the advantageous influence of the stress penumbra effect, a smallest cluster spacing optimizing model and a largest transformed volume cluster spacing optimizing model are built; the stress steering angle and the transformed volume are calculated; and finally, the optimal cluster spacing is determined by combining the optimized result of the smallest cluster spacing and the largest transformed volume cluster spacing. On the one hand, major fractures successively extend out, a horizontal well is segmentally fractured into a stratum to form the multiple major fractures, and on the other hand, the induced stress between the fractures is large as possible, so that branched fractures turn, the connectivity of natural fractures including the branched fractures and the major fractures is enhanced, a channel structure of oil gas flowing towards the major fractures is improved, and finally the purpose for improving the production capacity of an oil gas well is achieved.