Software development methodology has been being developed for the goal of improvement in productivity and reduction in time-to-market through the reuse of component asset, and software product line is designed for the effective management and use of the asset through the separation of commonality and variability. The existing methods that implement software product line interfere massively with the core asset, which require high cost in assembling level reducing the effectiveness. This paper introduces Aspect-Oriented Programming (AOP) as the method for the improvement of the assembling process in software product line. The method that assembles core asset and variabilities is described by grammar elements such as Join point, pointcut and advice without code-change. We analyze the requirements of the mini-system as an example adapting AOP and show its practicality by the implementation of Aspect-Oriented language, AspectJ