Petroleum exploration and production from Bakken and Three Forks formations in Williston Basin have achieved great momentum since 2005. To overcome the resistance of the low to extremely low permeability to hydrocarbons flow from reservoir to bottomhole, horizontal wells with multistage fracturing completion are applied to gain economical rate. Currently, horizontal lateral lengths that exceed 10,000 feet with more than 50 stages are not uncommon in Williston Basin. Field experience and practice indicate that different stage intervals usually results in different estimated ultimate recovery (EUR). Therefore, it is worth to identify optimal stage interval to stimulate horizontal lateral to cut costs through using the appropriate volumes of fracing fluid and proppant and to maximize profit by improving EUR. It should be noted that production from horizontal well with multistage fracturing is not only impacted by several factors such as geological characteristics, lateral length, orientation of horizontal lateral, fracing fluid, proppant, stimulation operating and procedure, and fracturing stage interval, but also by their interactions. To make the analysis reasonable, normalization analysis is exploited to differentiate the influences of different parameters. Sensitivity analysis of individual variable is applied to evaluate its influence on production. The analyses give a range of optimal stage interval for Bakken and Three Forks formations in different fields in Williston Basin. Considering the fact that variations in geology lead to different optimal stage intervals, it is appropriate to use a range instead of a single number as a reference in the well design. Although the results are derived from Bakken and Three Forks formations, the findings in this study can be employed in reservoirs with similar geological characteristics and reservoir properties. This study also identifies optimal ranges for operational parameters such as treatment pressure gradient, pumping rate, sand-to-water ratio, fracing fluid volume/length, and proppant mass/length, which are crucial to the cost reduction and operation efficiency.