Software metrics is a necessary step for software reliability and quality. Software metrics technique of traditional procedure-oriented programming is fairly maturity and has various methodologies and tools available for use. Object-oriented programming (OOP) becomes more popular. However, traditional procedure-oriented software metrics are not appropriate for the development of an object-oriented software. Some research of object-oriented software metrics has been proposed. Nevertheless, most of these metrics only focus on one specific characteristic of the object-oriented software. In this paper, a new metric methodology, the data scope complexity is proposed, for object-oriented software based on data scope of a program. The data scope complexity can present complexities of multiple features of object-oriented programming at the same time. Also, the advantages of OOP comparing with procedure-oriented programming are quantified and proved.