With the fast development of Internet, the runtime environment of computer software becomes on-limits gradually. Software dynamic evolution is going to be a hot research topic in software engineering area. The concept, which is called separation of concerns during the development of aspect-oriented software, can well support the dynamic evolution of software. Motivated by this, we propose a new model, called Aspect-Oriented Dynamic Software Architecture (AODSA), to support software dynamic evolution. The existing formal methods can not describe evolution process intuitively. Bigraph is a formal description language based on graphic which owns accurate and visual representation styles. We extend the existing Bigraph theory to represent AODSA. In order to signify the dynamic evolution of AODSA effectively, Bigraphical Reactive System (BRS) is applied to represent the evolution operation of AODSA. Meanwhile, the term language of Bigraph can describe the evolution operation of AODSA accurately which will lay the foundations for the further formal verification. Finally, a simple example is given to illustrate the usage of AODSA.