There are deep sandstone oil fields with large reserves in the South China Sea. The single well production using conventional development technology can not meet the economic threshold of offshore oil fields, which makes effective production difficult. Large-scale horizontal well fracturing technology is an important way to improve productivity and reduce economic threshold of offshore oil fields. However, staged fracturing of horizontal well also faces difficulties in fine geological design and fracturing scale design. Taking the deep reservoir of H Oilfield in the South China Sea as an example, through the analysis of geomechanical characteristics and fracturing feasibility, a reservoir classification method based on displacement pressure is proposed to solve the problem of characterization of ultimate capacity increase of natural seepage space after reservoir reconstruction for staged fracturing of horizontal wells, by constructing the evaluation model of index parameters. Aiming at the problems of fracture initiation difficulty and excessive extension in the fracturing of interbedded reservoir, through integrating the data of seismic, logging, experiment and technology, a comprehensive three-dimensional rock brittleness index characterization method is applied. The numerical model of combined fracture-height control fracturing is established, the fracture morphology and retrofit volume is predicted, and future productivity of wells is obtained. The research shows that high temperature resistant seawater based fracturing fluid is suitable for deep reservoir, and the type II reservoir with capacity of natural flow is the key of fracturing reconstruction. By matching the combined fracture-height control technology and the characteristics of thin interbedded reservoirs, the fractures can effectively initiate and extend moderately, which enhances the oil and gas seepage capacity between the natural reservoir and the hydraulic fractures. The single well productivity is released greatly, and the validity period is relatively long, which can reach more than 120 days at the initial stage of production. The research results provide a basis for large-scale development of offshore low permeability oil fields.