Taking Zhuanghai block 8 of the Guanjiapu Oilfield in shallow water as an example, this paper presents a 3D geological model of reservoir sand based on the reservoir description in the early period, and discusses some reservoir characters and horizontal development problems. The factors affecting the development behavior and production performance of horizontal wells, such as horizontal scale, horizontal orientation, parameters of horizontal segment, liquid rate and the optimum pattern of horizontal wells are aslo discussed. The results show that horizontal wells can be applied to the development of the field. The optimum plan for ground projects can avoid developing risk, shorten the developing construction period, and improve economic results.