We defined FCGlight, a refined version of the Fluid Construction Grammar (FCG), which is a formalism for studying the evolution of the natural language. We picked a core subset of FCG, and expressed it in the semantic framework of the Order-Sorted Features (OSF) logic. This allows for efficient processing, and also gives FCG a solid formal background for further analysis and improvement. Inspired from the conception of LIGHT[5], a system for natural language processing with large scale unification grammars, we developed a prototype system which implements FCGlight and can conduct language evolution experiments in a multi-agent population. We proved the functionalities of this system by running a experiment which models the evolution of the Russian verb aspect.