In the boom of unconventional resource exploration, horizontal completion has been widely used. Horizontal well has the advantages of increasing productivity index, preventing gas or water coning, avoiding sanding out, enhancing drainage area, reducing drilling pad and footprint, and accelerating recovery. Although these advantages have been well recognized over vertical completion, the quantitative contribution is not yet to be investigated. The current design of horizontal well is primarily derived from field experience. This consists of more or less arbitrary contents. To fill this gap, this paper presents a model to incorporate production from different lengths of horizontal well, cost of the drilling and completion, discount of revenue, and cost by different timing. The achieved optimum horizontal well design leads to a maximized net present value (NPV) for operators.