A computer simulation of the variable pressure growth chamber (VPGC) located at the NASA Johnson Space Center (JSC) has been developed using an expanded version of the Computer-Aided Systems Engineering and Analysis (CASE/A) simulation package. The VPGC is a pressure chamber that has been outfitted to support the growth of approximately 10.6 m2 of plants in an enclosed environment of approximately 27 m3 (Reference 1). CASE/A is a physical/chemical system-level simulation package originally developed to model the life support systems of Space Station Freedom. The expanded version of CASE/A extends the simulation package by including biological components, primarily plant growth algorithms. The configuration, modeling methods and verification of the CASE/A Variable Pressure Growth Chamber model are described. Performance estimates generated from the model are compared to data from recent lettuce growth experiments in the VPGC.