The process of pulping and papermaking is a complicated, resource-demanding operation that requires energy, water, and chemicals. When not managed properly, the process can also contribute significantly to pollution. The washing process is one critical operation that impacts the process's economics and environmental footprint. Most mills utilize rotary vacuum washers to separate black liquor from pulp, ensuring clean pulp for further processing downstream. Numerous factors influence the efficiency of a brown stock washer, and the washing operation itself is intricate. This study employs the system dynamics modeling approach to examine the critical role of brown stock washing in the pulp and paper industry, emphasizing optimizing process parameters for improved efficiency and sustainability. In the first part of the paper, a single stage of the washer system is modeled by establishing mass balance equations for key streams, including pulp, liquor, and dissolved solids. Within the system dynamics environment, separate models are developed for each stream, allowing for a detailed analysis of their behavior. To enhance modeling efficiency, the brown stock washing process is divided into four distinct operations: dilution, pulp formation, washing, and filtration. Breaking down the process into these operations makes it possible to focus on optimizing each step for improved overall performance. Furthermore, a control strategy is implemented to ensure stability in critical areas such as dilution vat level, discharged pulp consistency, and filtration tank level. In the final phase of the research, a multistage countercurrent brown stock washing line comprising three washers is modeled. Researchers can gain insights into how different components interact and influence overall performance by evaluating various parameters and analyzing the line's efficiency. This comprehensive analysis enables them to identify potential improvements and optimize the washing process for enhanced productivity and quality output. The conclusions drawn from this work offer valuable guidance for optimizing water management practices in the pulp and paper sector, contributing to the industry's sustainability goals and regulatory compliance.