Design of processor chips currently relies on the performance-oriented design method that focuses on hybrid optimizations among chip frequency, area and power consumption with multi-step and repetitive iterations via modern electronic design automation (EDA) techniques. Such conventional methodology results in significant costs, long period and high technical threshold. In this paper, we introduce an object-oriented architecture (OOA) paradigm with the idea borrowed from the software engineering area, and propose an OOA-based agile processor design methodology. Unlike the conventional performance-oriented design method, the proposed OOA-based agile design method mainly aims to shorten the development cycle, and to reduce the cost and complexity without sacrificing performance and reliability, which is evaluated as a new metric, agile degree. OOA expects to implement a series of decomposable, composable, and extensible objects in architectures of both general-purpose CPUs and application-specific XPUs via the object-oriented design paradigm, language and EDA tools. We further summary the research progress in each technical field covered by OOA, and analyze the challenges that may arise in the future research of OOA-based agile design methodology.