One key factor in the improved understanding of earth system science is the development and improvement of high fidelity models. Along with the deeper understanding of biogeophysical and biogeochemical processes, the software complexity of those earth system models becomes a barrier for further rapid model improvements and validation. In this paper, we present our experience on better understanding the Community Land Model (CLM) within an earth system modelling framework. First, we give an overview of the software system of the global offline CLM simulation. Second, we present our approach to better understand the CLM software structure and data structure using advanced software tools. After that, we focus on the practical issues related to CLM computational performance and individual ecosystem function. Since better software engineering practices are much needed for general scientific software systems, we hope those considerations can be beneficial to many other modeling research programs involving multiscale system dynamics.